💥 Remove the cosign information tag patching

[sergei-maertens]

The tag was introduced in Open Forms 2.3.0 and for backwards compatibility, a data migration and import conversion were added. The former has been removed a long time ago, the latter is being dropped now in OF 3.0.

Checklist

Check off the items that are completed or not relevant.

• Impact on features

  • Checked copying a form
  • Checked import/export of a form
  • Config checks in the configuration overview admin page
  • Problem detection in the admin email digest is handled

• Release management

  • I have labelled the PR as "needs-backport" accordingly

• I have updated the translations assets (you do NOT need to provide translations)

  • Ran ./bin/makemessages_js.sh
  • Ran ./bin/compilemessages_js.sh

• Dockerfile/scripts

  • Updated the Dockerfile with the necessary scripts from the ./bin folder

• Commit hygiene

  • Commit messages refer to the relevant Github issue
  • Commit messages explain the "why" of change, not the how

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.64%. Comparing base (eeae60c) to head (75372c0).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4975      +/-   ##
==========================================
- Coverage   96.65%   96.64%   -0.01%     
==========================================
  Files         762      761       -1     
  Lines       25927    25904      -23     
  Branches     3390     3385       -5     
==========================================
- Hits        25059    25036      -23     
  Misses        604      604              
  Partials      264      264              

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