Consider __doc__ always Optional. (#641)

python/mypy#2380 showed a discrepancy between object and FunctionType in stdlib2. The first defined __doc__ to be str, the second Optional[str]. As FunctionType depends on object, this is no longer valid.

As suggested by @gvanrossum in python/mypy#2380, all __doc__ should be considered Optional.

(Final verdict was just to remove most __doc__ attributes since it's inherited from object.)

stdlib/2/types.pyi

@@ -40,7 +40,6 @@ class FunctionType:
     __code__ = func_code
     __defaults__ = func_defaults
     __dict__ = func_dict
-    __doc__ = func_doc
     __globals__ = func_globals
     __name__ = func_name
     def __call__(self, *args: Any, **kwargs: Any) -> Any: ...