Clean up rkt specific code in `pkg/kubelet/pleg`
Clean up rkt specific code in `pkg/kubelet/pleg`

Clean up code in PLEG which was only necessary for the `rkt` runtime.

Rkt is no longer a built-in runtime and docker(shim) uses the CRI, so
its safe to remove this code entirely.

This diff removes the last mentions of `rkt` in the kubelet.

spzala/kubernetes,dims/kubernetes,mahak/kubernetes,joelsmith/kubernetes,zhouhaibing089/kubernetes,aveshagarwal/kubernetes,ixdy/kubernetes,du2016/kubernetes,dlorenc/kubernetes,PI-Victor/kubernetes,mosoft521/kubernetes,kevin-wangzefeng/kubernetes,u2takey/kubernetes,humblec/kubernetes,ingvagabund/kubernetes,fejta/kubernetes,johscheuer/kubernetes,MikeSpreitzer/kubernetes,joelsmith/kubernetes,xychu/kubernetes,tomzhang/kubernetes,shyamjvs/kubernetes,PI-Victor/kubernetes,jsafrane/kubernetes,cofyc/kubernetes,mfojtik/kubernetes,bparees/kubernetes,stevesloka/kubernetes,coolsvap/kubernetes,xlgao-zju/kubernetes,klaus1982/kubernetes,iameli/kubernetes,erwinvaneyk/kubernetes,chestack/kubernetes,soltysh/kubernetes,mikebrow/kubernetes,tallclair/kubernetes,mengqiy/kubernetes,dereknex/kubernetes,spzala/kubernetes,jdef/kubernetes,yujuhong/kubernetes,fgimenez/kubernetes,cofyc/kubernetes,maciaszczykm/kubernetes,kitt1987/kubernetes,rafax/kubernetes,jsafrane/kubernetes,k82/kubernetes,spzala/kubernetes,ravisantoshgudimetla/kubernetes,yarntime/kubernetes,ixdy/kubernetes,chrislovecnm/kubernetes,sanjeevm0/kubernetes,warmchang/kubernetes,sethpollack/kubernetes,iterion/kubernetes,jessfraz/kubernetes,joelsmith/kubernetes,JacobTanenbaum/kubernetes,u2takey/kubernetes,BenTheElder/kubernetes,weiwei04/kubernetes,Acidburn0zzz/kubernetes,k82cn/kubernetes,sethpollack/kubernetes,micahhausler/kubernetes,jdef/kubernetes,chestack/kubernetes,saad-ali/kubernetes,bparees/kubernetes,enj/kubernetes,aledbf/kubernetes,verb/kubernetes,bparees/kubernetes,tomzhang/kubernetes,PI-Victor/kubernetes,tcnghia/kubernetes,rrati/kubernetes,maciaszczykm/kubernetes,iterion/kubernetes,yarntime/kubernetes,LalatenduMohanty/kubernetes,lojies/kubernetes,x13n/kubernetes,andrewsykim/kubernetes,nak3/kubernetes,hex108/kubernetes,GulajavaMinistudio/kubernetes,Acidburn0zzz/kubernetes,wongma7/kubernetes,tpepper/kubernetes,tomerf/kubernetes,andrewsykim/kubernetes,maciaszczykm/kubernetes,pires/kubernetes,monopole/kubernetes,mkumatag/kubernetes,pweil-/kubernetes,nikhita/kubernetes,chestack/kubernetes,jfrazelle/kubernetes,weiwei04/kubernetes,jdef/kubernetes,ixdy/kubernetes,rrati/kubernetes,Clarifai/kubernetes,warmchang/kubernetes,zetaab/kubernetes,ravisantoshgudimetla/kubernetes,Acidburn0zzz/kubernetes,tomerf/kubernetes,thockin/kubernetes,jfrazelle/kubernetes,kevensen/kubernetes,LalatenduMohanty/kubernetes,pweil-/kubernetes,kevensen/kubernetes,thockin/kubernetes,jdef/kubernetes,kpgriffith/kubernetes,PiotrProkop/kubernetes,LalatenduMohanty/kubernetes,ravisantoshgudimetla/kubernetes,tpepper/kubernetes,ingvagabund/kubernetes,dlorenc/kubernetes,li-ang/kubernetes,BenTheElder/kubernetes,davidz627/kubernetes,nikhita/kubernetes,micahhausler/kubernetes,du2016/kubernetes,openshift/kubernetes,jfrazelle/kubernetes,mengqiy/kubernetes,monopole/kubernetes,tomzhang/kubernetes,GulajavaMinistudio/kubernetes,u2takey/kubernetes,MikeSpreitzer/kubernetes,yarntime/kubernetes,yarntime/kubernetes,ii/kubernetes,coolsvap/kubernetes,BenTheElder/kubernetes,kitt1987/kubernetes,kevensen/kubernetes,LalatenduMohanty/kubernetes,kpgriffith/kubernetes,davidz627/kubernetes,joelsmith/kubernetes,warmchang/kubernetes,jfrazelle/kubernetes,verult/kubernetes,mikebrow/kubernetes,xlgao-zju/kubernetes,zhouhaibing089/kubernetes,MHBauer/kubernetes,olivierlemasle/kubernetes,rnaveiras/kubernetes,jackfrancis/kubernetes,cblecker/kubernetes,huangjiuyuan/kubernetes,verult/kubernetes,warmchang/kubernetes,pmorie/kubernetes,thockin/kubernetes,iterion/kubernetes,luxas/kubernetes,davidz627/kubernetes,jfrazelle/kubernetes,linux-on-ibm-z/kubernetes,fanzhangio/kubernetes,Clarifai/kubernetes,u2takey/kubernetes,k82/kubernetes,tallclair/kubernetes,x13n/kubernetes,nikhita/kubernetes,stevesloka/kubernetes,Clarifai/kubernetes,pweil-/kubernetes,k82cn/kubernetes,hex108/kubernetes,mikedanese/kubernetes,xlgao-zju/kubernetes,mosoft521/kubernetes,monopole/kubernetes,stevesloka/kubernetes,kevensen/kubernetes,csrwng/kubernetes,kpgriffith/kubernetes,mYmNeo/kubernetes,huangjiuyuan/kubernetes,k82cn/kubernetes,zetaab/kubernetes,weiwei04/kubernetes,brendandburns/kubernetes,openshift/kubernetes,tcnghia/kubernetes,dims/kubernetes,spzala/kubernetes,huangjiuyuan/kubernetes,mboersma/kubernetes,wanghaoran1988/kubernetes,JacobTanenbaum/kubernetes,fgimenez/kubernetes,krmayankk/kubernetes,aledbf/kubernetes,mboersma/kubernetes,shyamjvs/kubernetes,linux-on-ibm-z/kubernetes,nikhita/kubernetes,mahak/kubernetes,kubernetes/kubernetes,lojies/kubernetes,mfojtik/kubernetes,MHBauer/kubernetes,yujuhong/kubernetes,fejta/kubernetes,PI-Victor/kubernetes,humblec/kubernetes,chrislovecnm/kubernetes,jessfraz/kubernetes,hex108/kubernetes,kitt1987/kubernetes,nak3/kubernetes,mkumatag/kubernetes,klaus1982/kubernetes,du2016/kubernetes,ixdy/kubernetes,nckturner/kubernetes,idvoretskyi/kubernetes,andrewsykim/kubernetes,xychu/kubernetes,ping035627/kubernetes,deads2k/kubernetes,mahak/kubernetes,mboersma/kubernetes,zhouhaibing089/kubernetes,jdef/kubernetes,pires/kubernetes,kubernetes/kubernetes,tallclair/kubernetes,sdminonne/kubernetes,idvoretskyi/kubernetes,matthyx/kubernetes,li-ang/kubernetes,k82cn/kubernetes,PiotrProkop/kubernetes,fanzhangio/kubernetes,aledbf/kubernetes,tomzhang/kubernetes,fabriziopandini/kubernetes,nak3/kubernetes,tcnghia/kubernetes,Lion-Wei/kubernetes,mikebrow/kubernetes,du2016/kubernetes,mahak/kubernetes,Acidburn0zzz/kubernetes,mfojtik/kubernetes,BenTheElder/kubernetes,aveshagarwal/kubernetes,ping035627/kubernetes,olivierlemasle/kubernetes,alejandroEsc/kubernetes,coolsvap/kubernetes,pweil-/kubernetes,kubernetes/kubernetes,tallclair/kubernetes,enj/kubernetes,wongma7/kubernetes,klaus1982/kubernetes,ravilr/kubernetes,mfojtik/kubernetes,MikeSpreitzer/kubernetes,saad-ali/kubernetes,andrewrynhard/kubernetes,hex108/kubernetes,johscheuer/kubernetes,andrewrynhard/kubernetes,klaus1982/kubernetes,mosoft521/kubernetes,shyamjvs/kubernetes,krmayankk/kubernetes,nckturner/kubernetes,JacobTanenbaum/kubernetes,mikedanese/kubernetes,tomzhang/kubernetes,jsafrane/kubernetes,saad-ali/kubernetes,tallclair/kubernetes,mengqiy/kubernetes,mkumatag/kubernetes,micahhausler/kubernetes,huangjiuyuan/kubernetes,wanghaoran1988/kubernetes,fgimenez/kubernetes,matthyx/kubernetes,aveshagarwal/kubernetes,tengqm/kubernetes,cblecker/kubernetes,sethpollack/kubernetes,BenTheElder/kubernetes,mboersma/kubernetes,tengqm/kubernetes,alejandroEsc/kubernetes,andrewrynhard/kubernetes,Clarifai/kubernetes,wongma7/kubernetes,Lion-Wei/kubernetes,tpepper/kubernetes,davidz627/kubernetes,csrwng/kubernetes,enj/kubernetes,GulajavaMinistudio/kubernetes,k82/kubernetes,davidz627/kubernetes,stevesloka/kubernetes,GulajavaMinistudio/kubernetes,kubernetes/kubernetes,jackfrancis/kubernetes,iameli/kubernetes,yujuhong/kubernetes,k82/kubernetes,JacobTanenbaum/kubernetes,liggitt/kubernetes,PiotrProkop/kubernetes,dixudx/kubernetes,ixdy/kubernetes,mikedanese/kubernetes,dims/kubernetes,ravisantoshgudimetla/kubernetes,mYmNeo/kubernetes,pmorie/kubernetes,MHBauer/kubernetes,olivierlemasle/kubernetes,johscheuer/kubernetes,kevensen/kubernetes,iameli/kubernetes,verb/kubernetes,verb/kubernetes,dixudx/kubernetes,aveshagarwal/kubernetes,sethpollack/kubernetes,ii/kubernetes,stevesloka/kubernetes,erwinvaneyk/kubernetes,mikebrow/kubernetes,joelsmith/kubernetes,sdminonne/kubernetes,bparees/kubernetes,chrislovecnm/kubernetes,tomerf/kubernetes,ravilr/kubernetes,saad-ali/kubernetes,wanghaoran1988/kubernetes,tengqm/kubernetes,luxas/kubernetes,yarntime/kubernetes,liggitt/kubernetes,idvoretskyi/kubernetes,aveshagarwal/kubernetes,Clarifai/kubernetes,cofyc/kubernetes,frodenas/kubernetes,tomzhang/kubernetes,dereknex/kubernetes,csrwng/kubernetes,jagosan/kubernetes,andrewrynhard/kubernetes,cmluciano/kubernetes,sanjeevm0/kubernetes,deads2k/kubernetes,carlory/kubernetes,frodenas/kubernetes,dixudx/kubernetes,dereknex/kubernetes,dixudx/kubernetes,andrewsykim/kubernetes,tpepper/kubernetes,ingvagabund/kubernetes,feiskyer/kubernetes,cmluciano/kubernetes,luxas/kubernetes,andrewsykim/kubernetes,ixdy/kubernetes,dlorenc/kubernetes,openshift/kubernetes,pires/kubernetes,hex108/kubernetes,nckturner/kubernetes,alejandroEsc/kubernetes,xlgao-zju/kubernetes,rafax/kubernetes,pwittrock/kubernetes,zetaab/kubernetes,fabriziopandini/kubernetes,deads2k/kubernetes,x13n/kubernetes,erwinvaneyk/kubernetes,coolsvap/kubernetes,mikebrow/kubernetes,brendandburns/kubernetes,ravilr/kubernetes,jessfraz/kubernetes,matthyx/kubernetes,ii/kubernetes,pmorie/kubernetes,mYmNeo/kubernetes,soltysh/kubernetes,sanjeevm0/kubernetes,cblecker/kubernetes,zetaab/kubernetes,verult/kubernetes,erwinvaneyk/kubernetes,tomzhang/kubernetes,krmayankk/kubernetes,wanghaoran1988/kubernetes,sdminonne/kubernetes,krmayankk/kubernetes,mfojtik/kubernetes,yujuhong/kubernetes,jingxu97/kubernetes,pires/kubernetes,PI-Victor/kubernetes,pmorie/kubernetes,cofyc/kubernetes,ravilr/kubernetes,cmluciano/kubernetes,k82/kubernetes,stevesloka/kubernetes,jessfraz/kubernetes,luxas/kubernetes,zetaab/kubernetes,tcnghia/kubernetes,zhangmingld/kubernetes,mkumatag/kubernetes,zhouhaibing089/kubernetes,fejta/kubernetes,ingvagabund/kubernetes,ping035627/kubernetes,chrislovecnm/kubernetes,verb/kubernetes,maciaszczykm/kubernetes,kevin-wangzefeng/kubernetes,tengqm/kubernetes,rafax/kubernetes,wongma7/kubernetes,sanjeevm0/kubernetes,ingvagabund/kubernetes,jingxu97/kubernetes,cblecker/kubernetes,openshift/kubernetes,cofyc/kubernetes,matthyx/kubernetes,iameli/kubernetes,tomerf/kubernetes,JacobTanenbaum/kubernetes,tpepper/kubernetes,pwittrock/kubernetes,openshift/kubernetes,xlgao-zju/kubernetes,iameli/kubernetes,li-ang/kubernetes,dlorenc/kubernetes,MikeSpreitzer/kubernetes,zhangmingld/kubernetes,sanjeevm0/kubernetes,humblec/kubernetes,csrwng/kubernetes,gnufied/kubernetes,pwittrock/kubernetes,brendandburns/kubernetes,dereknex/kubernetes,jessfraz/kubernetes,xychu/kubernetes,fgimenez/kubernetes,pweil-/kubernetes,verult/kubernetes,soltysh/kubernetes,ii/kubernetes,jingxu97/kubernetes,Clarifai/kubernetes,humblec/kubernetes,brendandburns/kubernetes,soltysh/kubernetes,kevin-wangzefeng/kubernetes,olivierlemasle/kubernetes,mboersma/kubernetes,GulajavaMinistudio/kubernetes,alejandroEsc/kubernetes,carlory/kubernetes,gnufied/kubernetes,johscheuer/kubernetes,u2takey/kubernetes,kevin-wangzefeng/kubernetes,jagosan/kubernetes,frodenas/kubernetes,LalatenduMohanty/kubernetes,frodenas/kubernetes,mosoft521/kubernetes,yujuhong/kubernetes,rnaveiras/kubernetes,huangjiuyuan/kubernetes,JacobTanenbaum/kubernetes,mYmNeo/kubernetes,lojies/kubernetes,lojies/kubernetes,kevin-wangzefeng/kubernetes,sdminonne/kubernetes,aledbf/kubernetes,tomzhang/kubernetes,pweil-/kubernetes,jackfrancis/kubernetes,rrati/kubernetes,roberthbailey/kubernetes,yujuhong/kubernetes,chrislovecnm/kubernetes,jagosan/kubernetes,lojies/kubernetes,li-ang/kubernetes,ravisantoshgudimetla/kubernetes,rnaveiras/kubernetes,maciaszczykm/kubernetes,fabriziopandini/kubernetes,verult/kubernetes,tcnghia/kubernetes,li-ang/kubernetes,coolsvap/kubernetes,idvoretskyi/kubernetes,mfojtik/kubernetes,shyamjvs/kubernetes,k82cn/kubernetes,zhangmingld/kubernetes,carlory/kubernetes,cofyc/kubernetes,dereknex/kubernetes,ii/kubernetes,iterion/kubernetes,kitt1987/kubernetes,aveshagarwal/kubernetes,ping035627/kubernetes,pwittrock/kubernetes,idvoretskyi/kubernetes,joelsmith/kubernetes,wongma7/kubernetes,linux-on-ibm-z/kubernetes,olivierlemasle/kubernetes,alejandroEsc/kubernetes,iterion/kubernetes,nckturner/kubernetes,feiskyer/kubernetes,rnaveiras/kubernetes,matthyx/kubernetes,chestack/kubernetes,coolsvap/kubernetes,cblecker/kubernetes,saad-ali/kubernetes,PiotrProkop/kubernetes,wanghaoran1988/kubernetes,luxas/kubernetes,mengqiy/kubernetes,mboersma/kubernetes,fejta/kubernetes,micahhausler/kubernetes,x13n/kubernetes,tomzhang/kubernetes,MHBauer/kubernetes,sdminonne/kubernetes,roberthbailey/kubernetes,zetaab/kubernetes,weiwei04/kubernetes,nak3/kubernetes,nak3/kubernetes,thockin/kubernetes,idvoretskyi/kubernetes,fanzhangio/kubernetes,spzala/kubernetes,jackfrancis/kubernetes,brendandburns/kubernetes,Lion-Wei/kubernetes,erwinvaneyk/kubernetes,Acidburn0zzz/kubernetes,pwittrock/kubernetes,liggitt/kubernetes,erwinvaneyk/kubernetes,sanjeevm0/kubernetes,MHBauer/kubernetes,kpgriffith/kubernetes,x13n/kubernetes,jagosan/kubernetes,mengqiy/kubernetes,kubernetes/kubernetes,zhouhaibing089/kubernetes,fabriziopandini/kubernetes,PI-Victor/kubernetes,tcnghia/kubernetes,tpepper/kubernetes,chestack/kubernetes,mYmNeo/kubernetes,enj/kubernetes,luxas/kubernetes,x13n/kubernetes,dims/kubernetes,carlory/kubernetes,liggitt/kubernetes,enj/kubernetes,jsafrane/kubernetes,fanzhangio/kubernetes,hex108/kubernetes,saad-ali/kubernetes,du2016/kubernetes,gnufied/kubernetes,tomerf/kubernetes,shyamjvs/kubernetes,thockin/kubernetes,mikedanese/kubernetes,carlory/kubernetes,xychu/kubernetes,krmayankk/kubernetes,xychu/kubernetes,u2takey/kubernetes,mYmNeo/kubernetes,dlorenc/kubernetes,monopole/kubernetes,kitt1987/kubernetes,zhangmingld/kubernetes,mahak/kubernetes,xychu/kubernetes,linux-on-ibm-z/kubernetes,kpgriffith/kubernetes,fgimenez/kubernetes,pires/kubernetes,csrwng/kubernetes,jingxu97/kubernetes,davidz627/kubernetes,zhangmingld/kubernetes,humblec/kubernetes,aledbf/kubernetes,verult/kubernetes,sethpollack/kubernetes,gnufied/kubernetes,fejta/kubernetes,iterion/kubernetes,nikhita/kubernetes,andrewsykim/kubernetes,rrati/kubernetes,Acidburn0zzz/kubernetes,ping035627/kubernetes,pwittrock/kubernetes,roberthbailey/kubernetes,brendandburns/kubernetes,fgimenez/kubernetes,zhangmingld/kubernetes,tengqm/kubernetes,feiskyer/kubernetes,feiskyer/kubernetes,linux-on-ibm-z/kubernetes,kitt1987/kubernetes,tomerf/kubernetes,pires/kubernetes,nak3/kubernetes,tallclair/kubernetes,mkumatag/kubernetes,maciaszczykm/kubernetes,frodenas/kubernetes,soltysh/kubernetes,roberthbailey/kubernetes,mikedanese/kubernetes,roberthbailey/kubernetes,dereknex/kubernetes,rrati/kubernetes,johscheuer/kubernetes,cmluciano/kubernetes,dixudx/kubernetes,krmayankk/kubernetes,dlorenc/kubernetes,bparees/kubernetes,jsafrane/kubernetes,kpgriffith/kubernetes,fanzhangio/kubernetes,Lion-Wei/kubernetes,Lion-Wei/kubernetes,cmluciano/kubernetes,weiwei04/kubernetes,rafax/kubernetes,chrislovecnm/kubernetes,micahhausler/kubernetes,huangjiuyuan/kubernetes,jingxu97/kubernetes,pmorie/kubernetes,cmluciano/kubernetes,yarntime/kubernetes,feiskyer/kubernetes,jagosan/kubernetes,pmorie/kubernetes,weiwei04/kubernetes,dims/kubernetes,fejta/kubernetes,ravisantoshgudimetla/kubernetes,jackfrancis/kubernetes,fabriziopandini/kubernetes,fanzhangio/kubernetes,PiotrProkop/kubernetes,andrewrynhard/kubernetes,verb/kubernetes,monopole/kubernetes,rnaveiras/kubernetes,xlgao-zju/kubernetes,mboersma/kubernetes,MikeSpreitzer/kubernetes,nckturner/kubernetes,mosoft521/kubernetes,liggitt/kubernetes,ravilr/kubernetes,ingvagabund/kubernetes,Lion-Wei/kubernetes,frodenas/kubernetes,johscheuer/kubernetes,warmchang/kubernetes,MHBauer/kubernetes,mboersma/kubernetes,deads2k/kubernetes,gnufied/kubernetes,LalatenduMohanty/kubernetes,wanghaoran1988/kubernetes,andrewrynhard/kubernetes,jdef/kubernetes,deads2k/kubernetes