Fix some "ruff check" warnings

[vstinner]

Remove unused import and variables.

[hugovk]

👍

We could add these Ruff checks to a CI lint as a followup to prevent new ones slipping in?

[StanFromIreland]

We could add these Ruff checks to a CI lint as a followup to prevent new ones slipping in?

I'd support adding pre-commit with a ruff hook (and possibly a few others, like trailing whitespace or zizmor).

[encukou]

In my opinion, this is a textbook example of unnecessary churn.

[vstinner]

I would like to fix these warnings to be able to run ruff check manually time to time to check for real bugs. Currently, the output is too verbose to be useful (because of the fixed issues).

[StanFromIreland]

I think adding specific ignores is worse than a little churn.