Clean up type annotations in caffe2/torch/nn/modules (#49957)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/49957
Test Plan: Sandcastle
Reviewed By: xush6528
Differential Revision: D25729745
fbshipit-source-id: 85810e2c18ca6856480bef81217da1359b63d8a3
