Remove uses and references to deprecated jwst.datamodels.DataModel

[braingram]

Closes #7574
This PR removes use of the deprecated and soon to be removed jwst.datamodels.DataModel from:

• a few tests: 5153670
• a check in blendmeta: c266d1e
• many docstrings
• some documentation pages (there are many remaining references to DataModel which appear to either not reference a page or reference a broken page).

Removing the uses here (and in crds: spacetelescope/crds#938) should allow us to remove the model from stdatamodels: spacetelescope/stdatamodels#171

Checklist for maintainers

• added entry in CHANGES.rst within the relevant release section
• updated or added relevant tests
• updated relevant documentation
• added relevant milestone
• added relevant label(s)
• ran regression tests, post a link to the Jenkins job below.
  How to run regression tests on a PR
• Make sure the JIRA ticket is resolved properly

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.01 ⚠️

Comparison is base (67ee6f4) 77.41% compared to head (7afd7e9) 77.40%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7607      +/-   ##
==========================================
- Coverage   77.41%   77.40%   -0.01%     
==========================================
  Files         455      455              
  Lines       36542    36542              
==========================================
- Hits        28288    28287       -1     
- Misses       8254     8255       +1     

Flag	Coverage Δ		*Carryforward flag
nightly	77.48% <ø> (-0.01%)	⬇️	Carriedforward from 67ee6f4

*This pull request uses carry forward flags. Click here to find out more.

Impacted Files	Coverage Δ
jwst/assign_wcs/assign_wcs.py	80.70% <ø> (ø)
jwst/assign_wcs/fgs.py	94.87% <ø> (ø)
jwst/assign_wcs/nircam.py	91.30% <ø> (ø)
jwst/assign_wcs/niriss.py	76.30% <ø> (ø)
jwst/assign_wcs/nirspec.py	94.03% <ø> (ø)
jwst/assign_wcs/util.py	83.86% <ø> (ø)
jwst/barshadow/bar_shadow.py	96.85% <ø> (ø)
jwst/combine_1d/combine1d.py	90.81% <ø> (ø)
jwst/extract_1d/apply_apcorr.py	95.75% <ø> (ø)
jwst/flatfield/flat_field.py	80.80% <ø> (ø)
... and 16 more

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.

[braingram]

Regression tests running at:
https://plwishmaster.stsci.edu:8081/job/RT/job/JWST-Developers-Pull-Requests/745/

[braingram]

Regression tests passed with no errors.

I'm not sure why the mac run on github took so long for the test_exec_time_many_crs. Going to close and reopen this to trigger the CI to see if the error reoccurs.

[hbushouse]

Looks like most changes are just in doc strings and hence harmless.