Move mutex_atomic to restriction

[rdrpenguin04]

By #4295, the general consensus seems to be that mutex_atomic is not a useful lint in most cases. If anything, it could be useful as a restriction on code that for whatever reason can't use atomics. Keeping it in clippy::nursery is harmful to people attempting to use clippy for soundness.

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changelog: Moved [mutex_atomic] to restriction
#10115

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @flip1995 (or someone else) soon.

Please see the contribution instructions for more information.

[flip1995]

If this lint is moved to restriction at least the documentation should summarize the discussions in the issue, why users of this lint should be careful.

[rdrpenguin04]

I have added a comment. I'm still not sure "shooting flies with cannons" is correct language for a formal issue description, but I didn't write it, and it's likely another PR's job to decide to replace it.

[flip1995]

@bors r+

Thanks! The description in the documentation LGTM.

[bors]

📌 Commit 0298095 has been approved by flip1995

It is now in the queue for this repository.

[bors]

⌛ Testing commit 0298095 with merge 6ccd4eb...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: flip1995
Pushing 6ccd4eb to master...