input: remove pxa930_trkball driver

The pxa930 SoC support is getting removed, and no upstream
board ever provided the trkball device that this driver
relies on.

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