[Don't review] Clean up type annotations in caffe2/torch/nn (#50079)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/50079
Test Plan: Sandcastle tests
Reviewed By: xush6528
Differential Revision: D25718694
fbshipit-source-id: f535fb879bcd4cb4ea715adfd90bbffa3fcc1150
