watchdog: adx_wdt.c: remove driver

Remove the driver (that was added in v2.6.32) since the architecture
has never been merged into mainline.

Reported-by: Paul Bolle <pebolle@tiscali.nl>
Acked-by: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>