Remove dead CAFFE2_LIBS variable (#31155)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31155
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Test Plan: Imported from OSS
Differential Revision: D19262584
Pulled By: ezyang
fbshipit-source-id: 147ac5a9c36e813ea9a2f68b498880942d661be5
