Drop unused imports from test (#49973)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/49973
From
```
./python/libcst/libcst codemod remove_unused_imports.RemoveUnusedImportsWithGlean --no-format caffe2/
```
Test Plan: Standard sandcastle tests
Reviewed By: xush6528
Differential Revision: D25727350
fbshipit-source-id: 237ec4edd85788de920663719173ebec7ddbae1c
