Unused functions

[braingram]

Resolves JP-nnnn
Resolves RCAL-nnnn

Closes #404
Closes #412
Closes #414
Closes #415
Closes #416
Closes #417 blocked by spacetelescope/jwst#9219

Regression tests: https://github.com/spacetelescope/RegressionTests/actions/runs/13506784800

Tasks

• update or add relevant tests
• update relevant docstrings and / or docs/ page
• Does this PR change any API used downstream? (if not, label with no-changelog-entry-needed)
  • write news fragment(s) in changes/: echo "changed something" > changes/<PR#>.<changetype>.rst (see below for change types)
  • run jwst regression tests with this branch installed ("git+https://github.com/<fork>/stdatamodels@<branch>")

news fragment change types...

• changes/<PR#>.feature.rst: new feature
• changes/<PR#>.bugfix.rst: fixes an issue
• changes/<PR#>.doc.rst: documentation change
• changes/<PR#>.removal.rst: deprecation or removal of public API
• changes/<PR#>.misc.rst: infrastructure or miscellaneous change

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 78.41%. Comparing base (4e83608) to head (dd02aab).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
src/stdatamodels/fits_support.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #420      +/-   ##
==========================================
+ Coverage   78.16%   78.41%   +0.24%     
==========================================
  Files         115      112       -3     
  Lines        5144     5101      -43     
==========================================
- Hits         4021     4000      -21     
+ Misses       1123     1101      -22     

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