os.system was never soft deprecated

[hugovk]

Follow on from #15179.

os.system was proposed to be soft deprecated (with some os methods) in a CPython issue and PR, but during the PR discussion, os.system was dropped from the PR.

See python/cpython#157882 for history.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[AlexWaygood]

Ah, thanks! I guess we looked at the PR title of that CPython change (which still mentions os.system()) but didn't look carefully enough at the actual diff

[AlexWaygood]

the actual docs change in that CPython PR does still harden the language around os.system() a little bit -- it now says that it's "recommended" to use the subprocess module instead. But I agree that that's probably a bit too weak to motivate marking it as deprecated in the stubs.