bpo-34802: Fix asyncio.iscoroutine() docs (GH-9611)

Doc/library/asyncio-task.rst

@@ -924,8 +924,7 @@ enforced.
    Return ``True`` if *obj* is a :ref:`coroutine object <coroutine>`.
 
    This method is different from :func:`inspect.iscoroutine` because
-   it returns ``True`` for generator-based coroutines decorated with
-   :func:`@coroutine <coroutine>`.
+   it returns ``True`` for generator-based coroutines.
 
 .. function:: iscoroutinefunction(func)