kill PyTorch py2 circle jobs (#29353)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/29353
First step to killing Python 2 everywhere. I don't really know that much
about the caffe2 circle jobs so I left them alone for now.
Test Plan: Imported from OSS
Differential Revision: D18920563
Pulled By: suo
fbshipit-source-id: b37d8427a6ecd4b8a7e16c1ff948e0ce13b5798f
