Removed unused import in proto file.
Removed unused import in proto file.

Importing 'mesos/resource_provider/resource_provider.proto' became
unnessecary after the cleanups in 'eeb09cbc1'.

Review: https://reviews.apache.org/r/64599/

asamerh4/mesos,Gilbert88/mesos,chhsia0/mesos,chhsia0/mesos,Gilbert88/mesos,reneploetz/mesos,kaysoky/mesos,andschwa/mesos,kaysoky/mesos,reneploetz/mesos,abudnik/mesos,abudnik/mesos,chhsia0/mesos,abudnik/mesos,dforsyth/mesos,dforsyth/mesos,gsantovena/mesos,abudnik/mesos,andschwa/mesos,dforsyth/mesos,asamerh4/mesos,reneploetz/mesos,Gilbert88/mesos,dforsyth/mesos,gsantovena/mesos,jpeach/mesos,kaysoky/mesos,kaysoky/mesos,jpeach/mesos,asamerh4/mesos,kaysoky/mesos,Gilbert88/mesos,gsantovena/mesos,jpeach/mesos,andschwa/mesos,reneploetz/mesos,andschwa/mesos,jpeach/mesos,jpeach/mesos,asamerh4/mesos,kaysoky/mesos,jpeach/mesos,asamerh4/mesos,chhsia0/mesos,gsantovena/mesos,chhsia0/mesos,Gilbert88/mesos,gsantovena/mesos,kaysoky/mesos,asamerh4/mesos,andschwa/mesos,Gilbert88/mesos,chhsia0/mesos,gsantovena/mesos,abudnik/mesos,dforsyth/mesos,Gilbert88/mesos,abudnik/mesos,abudnik/mesos,reneploetz/mesos,andschwa/mesos,jpeach/mesos,reneploetz/mesos,gsantovena/mesos,chhsia0/mesos,dforsyth/mesos,andschwa/mesos,asamerh4/mesos,reneploetz/mesos,dforsyth/mesos