Simplify benchmark patterns in mypy-strict.ini (#55700)
Summary:
These two lines were added in https://github.com/pytorch/pytorch/issues/53296, but they are needlessly complicated; this PR consolidates them.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/55700
Test Plan:
Run this command, and verify that the same number of files is given both before and after this PR:
```
mypy --config=mypy-strict.ini
```
Reviewed By: robieta
Differential Revision: D27684278
Pulled By: samestep
fbshipit-source-id: a34968cdff29cb8ad83813b277114224b5e37569
