fix stdatamodels datamodels link in documentation

[braingram]

Remove comment that made it's way into the data models docs and link to the now published stdatamodels docs.

Addresses comment: #7656 (comment)

Fixes: JP-3280

Link to updated datamodels docs built with this PR: https://jwst-pipeline--7657.org.readthedocs.build/en/7657/jwst/user_documentation/datamodels.html#jwst-datamodels

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 and project coverage have no change.

Comparison is base (403b9b3) 76.62% compared to head (515674b) 76.62%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7657   +/-   ##
=======================================
  Coverage   76.62%   76.62%           
=======================================
  Files         456      456           
  Lines       36831    36831           
=======================================
  Hits        28221    28221           
  Misses       8610     8610           

Flag	Coverage Δ		*Carryforward flag
nightly	77.43% <ø> (ø)		Carriedforward from 403b9b3

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[hbushouse]

Looks good. Docs built from this PR seem to have the correct link now.