remove useless self-assignment in folly::iobuf
remove useless self-assignment in folly::iobuf

Summary:
I'm pretty sure this doesn't do anything.

Based on a cursory review, I also don't think this is a bug (ie, it should have been assigned to something else).

Test Plan: fbconfig -r folly && fbmake runtests

Reviewed By: tudorb@fb.com

Subscribers: net-systems@, enis, folly-diffs@, yfeldblum, darshan, chalfant

FB internal diff: D2124497

Tasks: 7306976

Signature: t1:2124497:1433368083:1097dc22734dacad59b30d4b721be111d021bb43

floxard/folly,alexst07/folly,doctaweeks/folly,KSreeHarsha/folly,yangjin-unique/folly,PPC64/folly,bikong2/folly,bowlofstew/folly,bsampath/folly,bikong2/folly,gavioto/folly,lifei/folly,sonnyhu/folly,raphaelamorim/folly,Eagle-X/folly,juniway/folly,sonnyhu/folly,lifei/folly,Orvid/folly,Hincoin/folly,PoisonBOx/folly,juniway/folly,floxard/folly,sakishum/folly,sonnyhu/folly,leolujuyi/folly,mqeizi/folly,stonegithubs/folly,brunomorishita/folly,rklabs/folly,Eagle-X/folly,gaoyingie/folly,gavioto/folly,facebook/folly,Eagle-X/folly,gaoyingie/folly,chjp2046/folly,guker/folly,brunomorishita/folly,wildinto/folly,renyinew/folly,project-zerus/folly,Orvid/folly,SeanRBurton/folly,lifei/folly,rklabs/folly,gavioto/folly,reddit/folly,yangjin-unique/folly,fw1121/folly,xzmagic/folly,facebook/folly,arg0/folly,tempbottle/folly,stonegithubs/folly,juniway/folly,Hincoin/folly,project-zerus/folly,charsyam/folly,brunomorishita/folly,Hincoin/folly,CJstar/folly,clearlylin/folly,bobegir/folly,tempbottle/folly,gavioto/folly,guker/folly,zhiweicai/folly,arg0/folly,reddit/folly,facebook/folly,bikong2/folly,PoisonBOx/folly,charsyam/folly,nickhen/folly,theiver9827/folly,PPC64/folly,SammyK/folly,PPC64/folly,kernelim/folly,hongliangzhao/folly,clearlylin/folly,colemancda/folly,loversInJapan/folly,yangjin-unique/folly,brunomorishita/folly,renyinew/folly,gavioto/folly,SeanRBurton/folly,Orvid/folly,cole14/folly,bsampath/folly,shaobz/folly,PPC64/folly,Eagle-X/folly,tomhughes/folly,bsampath/folly,bobegir/folly,gaoyingie/folly,Orvid/folly,bobegir/folly,xzmagic/folly,kernelim/folly,chjp2046/folly,KSreeHarsha/folly,hongliangzhao/folly,doctaweeks/folly,bowlofstew/folly,mqeizi/folly,kernelim/folly,project-zerus/folly,colemancda/folly,CJstar/folly,arg0/folly,hongliangzhao/folly,cole14/folly,xzmagic/folly,floxard/folly,upsoft/folly,fw1121/folly,chjp2046/folly,sonnyhu/folly,tomhughes/folly,loversInJapan/folly,constantine001/folly,doctaweeks/folly,reddit/folly,charsyam/folly,zhiweicai/folly,tempbottle/folly,sakishum/folly,shaobz/folly,stonegithubs/folly,stonegithubs/folly,rklabs/folly,sonnyhu/folly,CJstar/folly,upsoft/folly,brunomorishita/folly,SammyK/folly,SeanRBurton/folly,CJstar/folly,theiver9827/folly,wildinto/folly,gaoyingie/folly,stonegithubs/folly,upsoft/folly,juniway/folly,SammyK/folly,rklabs/folly,PoisonBOx/folly,leolujuyi/folly,nickhen/folly,wildinto/folly,hongliangzhao/folly,SammyK/folly,guker/folly,arg0/folly,arg0/folly,bowlofstew/folly,reddit/folly,cole14/folly,PPC64/folly,zhiweicai/folly,raphaelamorim/folly,alexst07/folly,bsampath/folly,constantine001/folly,sakishum/folly,tomhughes/folly,zhiweicai/folly,renyinew/folly,CJstar/folly,rklabs/folly,lifei/folly,theiver9827/folly,fw1121/folly,SeanRBurton/folly,SammyK/folly,lifei/folly,guker/folly,gaoyingie/folly,KSreeHarsha/folly,Orvid/folly,chjp2046/folly,clearlylin/folly,kernelim/folly,zhiweicai/folly,constantine001/folly,bikong2/folly,bikong2/folly,nickhen/folly,fw1121/folly,guker/folly,wildinto/folly,raphaelamorim/folly,upsoft/folly,sakishum/folly,xzmagic/folly,doctaweeks/folly,cole14/folly,charsyam/folly,wildinto/folly,raphaelamorim/folly,tempbottle/folly,xzmagic/folly,reddit/folly,leolujuyi/folly,shaobz/folly,kernelim/folly,colemancda/folly,KSreeHarsha/folly,yangjin-unique/folly,colemancda/folly,leolujuyi/folly,bowlofstew/folly,mqeizi/folly,clearlylin/folly,nickhen/folly,floxard/folly,Eagle-X/folly,KSreeHarsha/folly,facebook/folly,floxard/folly,hongliangzhao/folly,tomhughes/folly,fw1121/folly,loversInJapan/folly,PoisonBOx/folly,bobegir/folly,sakishum/folly,theiver9827/folly,nickhen/folly,loversInJapan/folly,constantine001/folly,mqeizi/folly,upsoft/folly,constantine001/folly,project-zerus/folly,bobegir/folly,alexst07/folly,clearlylin/folly,alexst07/folly,bsampath/folly,alexst07/folly,cole14/folly,mqeizi/folly,tempbottle/folly,SeanRBurton/folly,yangjin-unique/folly,renyinew/folly,doctaweeks/folly,Hincoin/folly,leolujuyi/folly,chjp2046/folly,renyinew/folly,shaobz/folly,tomhughes/folly,raphaelamorim/folly,bowlofstew/folly,project-zerus/folly,Hincoin/folly,colemancda/folly,facebook/folly,PoisonBOx/folly,loversInJapan/folly,theiver9827/folly,juniway/folly,shaobz/folly