Always import Protocol from typing in stubs (#6617)

stdlib/dataclasses.pyi

@@ -1,7 +1,6 @@
 import sys
 import types
-from typing import Any, Callable, Generic, Iterable, Mapping, Tuple, Type, TypeVar, overload
-from typing_extensions import Protocol
+from typing import Any, Callable, Generic, Iterable, Mapping, Protocol, Tuple, Type, TypeVar, overload
 
 if sys.version_info >= (3, 9):
     from types import GenericAlias