Drop unused imports from caffe2/quantization (#50493)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/50493
Pull Request resolved: https://github.com/pytorch/pytorch/pull/49974
From
```
./python/libcst/libcst codemod remove_unused_imports.RemoveUnusedImportsWithGlean --no-format caffe2/
```
Test Plan: Sandcastle Tests
Reviewed By: xush6528
Differential Revision: D25902417
fbshipit-source-id: aeebafce2c4fb649cdce5cf4fd4c5b3ee19923c0
