Never explicitly inherit from object in Python 3-only stubs (#6777)

stdlib/threading.pyi

@@ -34,7 +34,7 @@ TIMEOUT_MAX: float
 
 class ThreadError(Exception): ...
 
-class local(object):
+class local:
     def __getattribute__(self, name: str) -> Any: ...
     def __setattr__(self, name: str, value: Any) -> None: ...
     def __delattr__(self, name: str) -> None: ...