Tiny clean up of reducer_functors
Tiny clean up of reducer_functors

Summary: Just to make life a bit easier to further work.

Reviewed By: kennyhorror

Differential Revision: D4388071

fbshipit-source-id: 71b99ef1c2dc680afe4e9ef2f7a370e43116ce99

Yangqing/caffe2,xzturn/caffe2,sf-wind/caffe2,Yangqing/caffe2,xzturn/caffe2,davinwang/caffe2,pietern/caffe2,Yangqing/caffe2,pietern/caffe2,pietern/caffe2,xzturn/caffe2,pietern/caffe2,caffe2/caffe2,sf-wind/caffe2,bwasti/caffe2,bwasti/caffe2,bwasti/caffe2,Yangqing/caffe2,pietern/caffe2,xzturn/caffe2,Yangqing/caffe2,davinwang/caffe2,bwasti/caffe2,davinwang/caffe2,bwasti/caffe2,davinwang/caffe2,davinwang/caffe2,sf-wind/caffe2,sf-wind/caffe2,xzturn/caffe2,sf-wind/caffe2