Update typing_extensions imports in third-party stubs (#11245)

stubs/waitress/waitress/buffers.pyi

@@ -1,6 +1,5 @@
 from io import BufferedIOBase, BufferedRandom, BytesIO
-from typing import Any
-from typing_extensions import Literal
+from typing import Any, Literal
 
 COPY_BYTES: int
 STRBUF_LIMIT: int

stubs/waitress/waitress/compat.pyi

@@ -1,6 +1,5 @@
 from io import TextIOWrapper
-from typing import Any
-from typing_extensions import Literal
+from typing import Any, Literal
 
 PY2: Literal[False]
 PY3: Literal[True]

stubs/waitress/waitress/trigger.pyi

@@ -2,7 +2,7 @@ import sys
 from collections.abc import Callable, Mapping
 from socket import socket
 from threading import Lock
-from typing_extensions import Literal
+from typing import Literal
 
 from waitress import wasyncore as wasyncore