Update docs for master to remove Python 2 references (#36114)
Summary:
Full details in task: https://our.intern.facebook.com/intern/tasks/?t=64776265
With pytroch 1.5+ we remove python2 support from PyTorch. All documentation under docs/ and on the pytorch.org website needs to remove Python 2 references.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/36114
Differential Revision: D20901746
Pulled By: jlin27
fbshipit-source-id: 07f8dc8e6fab0b232e5048a63079cab0c433c85f
