Revert "stubtest pos-only differences in dunders (#12184)"

[hauntsaninja]

This reverts commit 777885f.

To help with python/typeshed#7441 and reduce risk of stubtest issues interfering with a mypy release. The extra type correctness here is really minimal.

[github-actions]

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

[JelleZijlstra]

Always glad when mypy-primer confirms that changing stubtest doesn't affect typechecking output.

Though maybe we need a stubtest-primer that tells us stubtest's output on all of typeshed's third-party stubs.

[AlexWaygood]

Thanks! I agree this was the way to go :)

[AlexWaygood]

[M]aybe we need a stubtest-primer that tells us stubtest's output on all of typeshed's third-party stubs.

Yes, I think this would be very helpful. Something similar to the "Daily test" job in the typeshed CI, that's run on every stubtest PR, would be amazing. (Edit: it would obviously have to be done in a non-blocking way, like mypy_primer.)