multiprocessing.resource_sharer: remove unused TypeAlias (#8424)

stdlib/multiprocessing/resource_sharer.pyi

@@ -1,13 +1,8 @@
 import sys
 from socket import socket
-from typing import Union
-from typing_extensions import TypeAlias
 
 __all__ = ["stop"]
 
-# https://docs.python.org/3/library/multiprocessing.html#address-formats
-_Address: TypeAlias = Union[str, tuple[str, int]]
-
 if sys.platform == "win32":
     __all__ += ["DupSocket"]