Clean up some type annotations in torch/jit (#49939)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/49939
Upgrades type annotations from Python2 to Python3
Test Plan: Sandcastle tests
Reviewed By: xush6528
Differential Revision: D25717573
fbshipit-source-id: 7d5c98fafaa224e0504b73dc69b1e4a6410c0494
