Remove CAFFE2_CPU_FLAGS
Remove CAFFE2_CPU_FLAGS

Summary:
Since this is only a duplicate of CMAKE_CXX_FLAGS we should simplify the set of options.
Closes https://github.com/caffe2/caffe2/pull/1327

Differential Revision: D6031544

Pulled By: Yangqing

fbshipit-source-id: 5c610a70118089b4d96be30ab028ef1d5efdb019

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