Remove prefix from websocket handler name

Remove the websocket prefix "websocket_handler_" introduced in
761eef7. Makes url_for() unable to find the corresponding ws route.

sanic/app.py

@@ -494,9 +494,7 @@ def response(handler):
             websocket_handler = partial(
                 self._websocket_handler, handler, subprotocols=subprotocols
             )
-            websocket_handler.__name__ = (
-                "websocket_handler_" + handler.__name__
-            )
+            websocket_handler.__name__ = handler.__name__
             routes.extend(
                 self.router.add(
                     uri=uri,