remove unused imports and variables

[zacharyburnett]

apply Ruff rules F841 and F401 to the excluded modules jwst/fits_generator and jwst/associations

Checklist for PR authors (skip items if you don't have permissions or they are not applicable)

• [x] ~added entry in CHANGES.rst within the relevant release section~
• [x] ~updated or added relevant tests~
• [x] ~updated relevant documentation~
• [ ] added relevant milestone
• [x] added relevant label(s)
• [ ] ran regression tests, post a link to the Jenkins job below. How to run regression tests on a PR
• [ ] All comments are resolved
• [x] ~Make sure the JIRA ticket is resolved properly~

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 59.59%. Comparing base (ccf871a) to head (3ac4be4). Report is 9 commits behind head on master.

Files	Patch %	Lines
jwst/fits_generator/template.py	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #8651 +/- ## ========================================== + Coverage 59.56% 59.59% +0.02% ========================================== Files 391 391 Lines 39285 39267 -18 ========================================== Hits 23402 23402 + Misses 15883 15865 -18 ```

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[zacharyburnett]

this PR is superseded by #8652, unless we want to only apply the import-related fixes to these modules without un-excluding them

[emolter]

I don't see anything wrong with un-excluding them and going with #8652