Update outdated handle_request docstring (#2100)

sanic/app.py

@@ -664,11 +664,6 @@ class Sanic(BaseSanic):
         exception handling must be done here
 
         :param request: HTTP Request object
-        :param write_callback: Synchronous response function to be
-            called with the response as the only argument
-        :param stream_callback: Coroutine that handles streaming a
-            StreamingHTTPResponse if produced by the handler.
-
         :return: Nothing
         """
         # Define `response` var here to remove warnings about