remove decode()
remove decode()

Summary: This should not be needed any more since we use pybind. It will help python3 migration.

Reviewed By: salexspb

Differential Revision: D4535490

fbshipit-source-id: a47615f73b5c35b940d21bb2d5d55060fa0850be

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