Remove flake8-rst usage
This is required to make all the tests pass and merge #51827

As background, flake8-rst is breaking on python3.10, and the repository has not been maintained since December 2020:
[https://pypi.org/project/flake8-rst/#history](url)
@MarcoGorelli Here is the PR for the flake8-rst removal. Once merged I will update #51827 by merging it to main and push.