Remove subcategory enums from program and l3_common

[braingram]

Closes #889

Removes the subcategory enums in program and l3_common.

Regression tests:
https://github.com/spacetelescope/RegressionTests/actions/runs/28548621560
show 2 expected differences for tvac data where subcategory is ? with this PR instead of CAL on main (both from the use of create_fake_data in processing tvac data).

Tasks

• Update or add relevant rad tests.
• Update relevant docstrings and / or docs/ page.
• Does this PR change any schema files?
  • Schema changes were discussed at RAD Review Board meeting.
• 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).
  • Start a romancal regression test (https://github.com/spacetelescope/RegressionTests/actions/workflows/romancal.yml) with this branch installed ("git+https://github.com/<fork>/rad@<branch>").
  • Update relevant roman_datamodels utilities and tests.

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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.03%. Comparing base (5e16410) to head (4dbd729).
⚠️ Report is 14 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #893      +/-   ##
==========================================
- Coverage   86.56%   86.03%   -0.54%     
==========================================
  Files          15       15              
  Lines        1154     1131      -23     
==========================================
- Hits          999      973      -26     
- Misses        155      158       +3     

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