mypy: remove has_member (#8438)
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())
```
