ci(submodule): remove config for updating old 2.x repo (backport #1182)

[mergify[bot]]

This is an automatic backport of pull request #1182 done by Mergify. Cherry-pick of 58c991ad3e11a4a8686a86c54a254bf1943a3beb has failed:

On branch mergify/bp/cryostat-v2.4/pr-1182
Your branch is up to date with 'origin/cryostat-v2.4'.

You are currently cherry-picking commit 58c991a.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
    both modified:   .github/workflows/submodule.yaml

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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[andrewazores]

Not needed.