[pytorch] Remove python2 support from tests and torch.jit (#35042)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/35042
Removing python2 tests and some compat code in torch.jit. Check if dependent projects and external tests have any issues after these changes.
Test Plan: waitforsandcastle
Reviewed By: suo, seemethere
Differential Revision: D18942633
fbshipit-source-id: d76cc41ff20bee147dd8d44d70563c10d8a95a35
