tty: moxa: remove driver.

This is a very old driver, and no known hardware is still around for it,
and the company says they do not need it anymore, so let's remove it as
the LLMs are starting to poke at it and find "interesting" things which
will just waste everyone's time given it's not actually used.

So let's drop it.  If someone really needs it, it can come back in the
future, in a more "modern" way, as the style here is very old...

Reported-by: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/all/afqyY8FQ8ZfpH48_@moxa-ThinkCentre-M90t/
Acked-by: Crescent Hsieh <crescentcy.hsieh@moxa.com>
Acked-by: Jiri Slaby <jirislaby@kernel.org>
Link: https://patch.msgid.link/20260804-x-remove-moxa-v2-1-947c039b66e8@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>