Removed unused variable in libprocess.
Removed unused variable in libprocess.

Review: https://reviews.apache.org/r/42974/

dforsyth/mesos,gsantovena/mesos,andschwa/mesos,verizonlabs/mesos,andschwa/mesos,gsantovena/mesos,kaysoky/mesos,Aman-Jain-14/customizedMesos,neilconway/mesos,kaysoky/mesos,jpeach/mesos,yuquanshan/customizedMesos,jpeach/mesos,chhsia0/mesos,zmalik/mesos,jpeach/mesos,gsantovena/mesos,verizonlabs/mesos,abudnik/mesos,asamerh4/mesos,andschwa/mesos,asamerh4/mesos,jpeach/mesos,zmalik/mesos,andschwa/mesos,chhsia0/mesos,abudnik/mesos,reneploetz/mesos,andschwa/mesos,gsantovena/mesos,reneploetz/mesos,neilconway/mesos,zmalik/mesos,reneploetz/mesos,reneploetz/mesos,asamerh4/mesos,dforsyth/mesos,yuquanshan/customizedMesos,neilconway/mesos,yuquanshan/customizedMesos,neilconway/mesos,Aman-Jain-14/customizedMesos,Aman-Jain-14/customizedMesos,craimbert/mesos,Gilbert88/mesos,kaysoky/mesos,Gilbert88/mesos,andschwa/mesos,asamerh4/mesos,dforsyth/mesos,dforsyth/mesos,yuquanshan/customizedMesos,Gilbert88/mesos,jpeach/mesos,verizonlabs/mesos,abudnik/mesos,Gilbert88/mesos,dforsyth/mesos,craimbert/mesos,Gilbert88/mesos,verizonlabs/mesos,verizonlabs/mesos,chhsia0/mesos,neilconway/mesos,zmalik/mesos,kaysoky/mesos,neilconway/mesos,asamerh4/mesos,Gilbert88/mesos,Aman-Jain-14/customizedMesos,dforsyth/mesos,craimbert/mesos,chhsia0/mesos,neilconway/mesos,zmalik/mesos,kaysoky/mesos,reneploetz/mesos,gsantovena/mesos,craimbert/mesos,abudnik/mesos,craimbert/mesos,asamerh4/mesos,chhsia0/mesos,kaysoky/mesos,yuquanshan/customizedMesos,abudnik/mesos,reneploetz/mesos,zmalik/mesos,Gilbert88/mesos,zmalik/mesos,gsantovena/mesos,Aman-Jain-14/customizedMesos,kaysoky/mesos,gsantovena/mesos,craimbert/mesos,asamerh4/mesos,craimbert/mesos,chhsia0/mesos,jpeach/mesos,dforsyth/mesos,Aman-Jain-14/customizedMesos,yuquanshan/customizedMesos,chhsia0/mesos,verizonlabs/mesos,verizonlabs/mesos,abudnik/mesos,yuquanshan/customizedMesos,Aman-Jain-14/customizedMesos,reneploetz/mesos,jpeach/mesos,andschwa/mesos,abudnik/mesos