[Needs Review] Convert some files to Python3 (#49351)
Summary:
Uses the Python standard library 2to3 script to convert a number of Python 2 files to Python 3. This facilitates code maintenance such as dropping unused imports in D25500422.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/49351
Test Plan: Standard sandcastle tests
Reviewed By: xush6528
Differential Revision: D25499576
fbshipit-source-id: 0c44718ac734771ce0758b1cb30676cc3d76ac10
