remove AssociationsModel

[braingram]

Requires spacetelescope/romancal#1954

Removes the unused AssociationsModel.

See spacetelescope/romancal#1846 for more details.

Regtests all pass: https://github.com/spacetelescope/RegressionTests/actions/runs/17917081333

Tasks

• Update or add relevant roman_datamodels 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).
  • 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>").

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 95.57%. Comparing base (087a60d) to head (291ecb1).
⚠️ Report is 189 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #562      +/-   ##
==========================================
- Coverage   97.56%   95.57%   -1.99%     
==========================================
  Files          30       41      +11     
  Lines        2788     4160    +1372     
==========================================
+ Hits         2720     3976    +1256     
- Misses         68      184     +116     

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[WilliamJamieson]

Do you think we need this

roman_datamodels/tests/test_open.py

Lines 240 to 257 in 867de77

	def test_open_asn(tmp_path):
	romancal = pytest.importorskip("romancal")
	fn = tmp_path / "test.json"
	asn = {
	"products": [
	{
	"members": [],
	"name": "foo",
	}
	],
	}
	with open(fn, "w") as f:
	json.dump(asn, f)
	lib = datamodels.open(fn)
	assert isinstance(lib, romancal.datamodels.ModelLibrary)

test anymore? If not we may want to remove it and all the "with romancal" related CI jobs

Never mind I thought that was using this model to open the ASN.

[PaulHuwe]

LGTM