input: remove pxa930_rotary keyboard driver

The pxa930 platform is getting removed and no upstream machine
ever defined a rotary keyboard device.

Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: linux-input@vger.kernel.org
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>