[BE] Enable flake8-simplify checks (#97984)
Enable some sensible flake8-simplify rules. Mainly wanted to enable the SIM101, and `yield from` SIM103 checks. @kit1980 since you wanted to be tagged on this CI check.
Enabling this check also helped flag one logical bug so it's definitely beneficial (also fixed in this PR).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/97984
Approved by: https://github.com/ezyang
