Remove warning about asyncio being provisional (it's not in 3.5 and up).

Doc/library/asyncio.rst

@@ -4,13 +4,6 @@
 .. module:: asyncio
    :synopsis: Asynchronous I/O, event loop, coroutines and tasks.
 
-.. note::
-
-   The asyncio package has been included in the standard library on a
-   :term:`provisional basis <provisional package>`. Backwards incompatible
-   changes (up to and including removal of the module) may occur if deemed
-   necessary by the core developers.
-
 .. versionadded:: 3.4
 
 **Source code:** :source:`Lib/asyncio/`