Summary:
This PR greatly simplifies `mypy-strict.ini` by strictly typing everything in `.github` and `tools`, rather than picking and choosing only specific files in those two dirs. It also removes `warn_unused_ignores` from `mypy-strict.ini`, for reasons described in https://github.com/pytorch/pytorch/pull/56402#issuecomment-822743795: basically, that setting makes life more difficult depending on what libraries you have installed locally vs in CI (e.g. `ruamel`).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/59117
Test Plan:
```
flake8
mypy --config mypy-strict.ini
```
Reviewed By: malfet
Differential Revision: D28765386
Pulled By: samestep
fbshipit-source-id: 3e744e301c7a464f8a2a2428fcdbad534e231f2e
