RAD-243: Remove MA Table Keys from Dark

[PaulHuwe]

Resolves RAD-243

Closes #771

This PR removes the MA Table keywords from the dark current reference schema.

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

[PaulHuwe]

RCAL Regression tests pass:
https://github.com/spacetelescope/RegressionTests/actions/runs/19995224941

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.87%. Comparing base (6ab0be9) to head (d22bfd4).
⚠️ Report is 66 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #776   +/-   ##
=======================================
  Coverage   85.87%   85.87%           
=======================================
  Files          14       14           
  Lines        1069     1069           
=======================================
  Hits          918      918           
  Misses        151      151           

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[schlafly]

This looks fine to me.