Remove psutil from requirements.txt (backport #894)

[mergify]

Summary

Remove psutil since it is not used in the project (was it ever used btw? Even first tag does not seem to use this package at all.)

Details and comments

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This is an automatic backport of pull request #894 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 06075c1 has failed:

On branch mergify/bp/stable/0.8/pr-894
Your branch is up to date with 'origin/stable/0.8'.

You are currently cherry-picking commit 06075c1.
  (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:   requirements.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