[7.17](backport #39939) Remove requirements_aix.txt

[mergify]

We do not test this file and CVE scans in the repository will flag packages in it. Rather than keep it up to date with no testing, just delete it.

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This is an automatic backport of pull request #39939 done by Mergify.

[mergify]

Cherry-pick of 2f10d08 has failed:

On branch mergify/bp/7.17/pr-39939
Your branch is up to date with 'origin/7.17'.

You are currently cherry-picking commit 2f10d08403.
  (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/rm <file>..." as appropriate to mark resolution)
	deleted by them: libbeat/tests/system/requirements_aix.txt

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/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[botelastic]

This pull request doesn't have a Team:<team> label.