Migrate TL adapter utils tests to non-fb location and drop shims

[saitcakmak]

Summary:
The TL adapter utilities get_joint_search_space, merge_dependents, merge_parameters (in ax/adapter/transfer_learning/utils.py) and get_mapped_parameter_names (in ax/adapter/transfer_learning/utils_torch.py) were previously migrated out of ax/fb/adapter/, which left behind pure re-export shims at ax/fb/adapter/utils.py and ax/fb/adapter/utils_torch.py. The only remaining coverage for these functions lived in ax/fb/adapter/tests/test_utils.py and test_utils_torch.py, exercising the migrated code through those shims -- and the non-fb destination had no test coverage of its own.

This moves both test files to ax/adapter/transfer_learning/tests/, switches their imports to the real non-fb modules (ax.adapter.transfer_learning.utils/utils_torch, ax.core.auxiliary_source.AuxiliarySource, ax.utils.common.testutils.TestCase), and removes the now-unused get_unordered_choice/get_ordered_choice helpers from test_utils.py.

Since the two test files were the only callers of the ax.fb.adapter.utils/utils_torch shims repo-wide, the shims are deleted and the BUCK targets are updated accordingly: a new test_utils python_unittest is added under ax/adapter/transfer_learning/BUCK, and the old test_utils target, the orphaned :utils library, and the utils_torch.py src are removed from ax/fb/adapter/BUCK.

The broader ax.fb.core.auxiliary_source shim is left in place; it still has many callers across admarket, pts, automl, storage, and docs, so cleaning it up is a separate effort.

Differential Revision: D107429272

[meta-codesync]

@saitcakmak has exported this pull request. If you are a Meta employee, you can view the originating Diff in D107429272.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.57%. Comparing base (d0ae700) to head (b658583).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5217      +/-   ##
==========================================
+ Coverage   96.50%   96.57%   +0.07%     
==========================================
  Files         617      619       +2     
  Lines       69776    69904     +128     
==========================================
+ Hits        67339    67512     +173     
+ Misses       2437     2392      -45     

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[meta-codesync]

This pull request has been merged in 779b245.