Clean up type annotations in caffe2/torch/nn/modules (#49938)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/49938
Test Plan: Sandcastle tests
Reviewed By: xush6528
Differential Revision: D25718705
fbshipit-source-id: 6a9e3e6d17aa458726cd32aa0a71a63c51b601d9
