Add rule for fixing imports which use as with a no-op

[kkirsche]

For example:

from example.fixit_ex import ExampleClass as ExampleClass

Should be:

from example.fixit_ex import ExampleClass

Because using as with the same resulting name is a no-operation action.

[Zac-HD]

mypy treats it differently though, and other type-checkers might too. I prefer using __all__ but I'd hesitate to autofix this unless the tool has decided to enforce that preference (like shed does).

[amyreese]

This would be a good fit for the new extra rules package in Fixit 2.0.