Clean up some type annotations in torch/testing/_internal (#50078)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/50078
Upgrades type annotations from Python2 to Python3
Test Plan: Sandcastle tests
Reviewed By: pritamdamania87
Differential Revision: D25717560
fbshipit-source-id: cec631f3121ef9ab87ff8b3b00f1fae6df9a2155
