Remove unused optimizers
Remove unused optimizers

Summary: As desc.

Reviewed By: xianjiec

Differential Revision: D4840482

fbshipit-source-id: bf820154475508ce581d16a45bcd93d026b60f30

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