[3.10] bpo-44559: [Enum] revert enum module to 3.9 (GH-27010)

* [Enum] revert enum module to 3.9

Author: ethanfurman

Doc/howto/enum.rst

@@ -17,7 +17,6 @@ Currently, the HOWTOs are:
    cporting.rst
    curses.rst
    descriptor.rst
-   enum.rst
    functional.rst
    logging.rst
    logging-cookbook.rst