mypy: remove has_member

[hauntsaninja]

In particular:

• The test case mentioned in the code passes without it
• The test case changed seems to have more desirable behaviour now,
  consider:

from typing import Any

"""
class C:
    def __radd__(self, other) -> float:
        return 1.234
"""
C: Any
class D(C):
    pass

reveal_type("str" + D())

[JukkaL]

Thanks! I agree that it looks like has_member can now be safely removed.

@Michael0x2a In case you think that the comment is still valid and this isn't something we should do, we can reconsider this change.

[Michael0x2a]

If all the tests are now passing/the metaclass thing no longer seems to be an issue, I agree merging this seems like a good idea.

I do remember filing an issue related to this in #5491 -- it could be worth double-checking to see if we also still need to keep that open.