remove pytest asdf plugin configuration for non-existant schemas

[braingram]

The pyproject.toml file contains configuration for the pytest asdf plugin (for testing schemas):

romancal/pyproject.toml

Lines 135 to 137 in 459e8e3

	asdf_schema_tests_enabled = true
	asdf_schema_validate_default = false
	asdf_schema_root = "romancal/datamodels/schemas"

However there is no romancal/datamodels/schemas (the schemas exist and are tested in rad).

This PR removes the unnecessary configuration.

With this PR pytest finds 854 test items:
https://github.com/spacetelescope/romancal/actions/runs/9958232059/job/27512161042?pr=1305#step:10:154
the same number is found on main:
https://github.com/spacetelescope/romancal/actions/runs/9893953303/job/27330394884#step:10:154
verifying that no schemas are found for testing and that the configuration removed in this PR was doing nothing (but was adding an implicit dependency on the asdf pytest plugin).

Checklist

• added entry in CHANGES.rst under the corresponding subsection
• updated relevant tests
• updated relevant documentation
• updated relevant milestone(s)
• added relevant label(s)
• ran regression tests, post a link to the Jenkins job below. How to run regression tests on a PR

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.37%. Comparing base (7f4bc19) to head (05bfe45).
Report is 251 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1305   +/-   ##
=======================================
  Coverage   79.37%   79.37%           
=======================================
  Files         117      117           
  Lines        8086     8086           
=======================================
  Hits         6418     6418           
  Misses       1668     1668           

Flag	Coverage Δ		*Carryforward flag
nightly	62.86% <ø> (ø)		Carriedforward from 4ae77c7

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[schlafly]

Looks good to me, thanks!

[braingram]

Closing and re-opening to re-trigger the CI now that I wiped the webbpsf cache.

[braingram]

@schlafly I'm not sure if closing and re-opening (to fix the bad webbpsf cache) dismissed your approval. Was this previously approved? If so, would you re-approve it?