Remove python2 support from setup.py (#35539)
Summary:
As a followup to https://github.com/pytorch/pytorch/pull/35042 this removes python2 from setup.py and adds Python 3.8 to the list of supported versions. We're already testing this in CircleCI.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/35539
Differential Revision: D20709060
Pulled By: orionr
fbshipit-source-id: 5d40bc14cb885374fec370fc7c5d3cde8769039a
