watchdog: iTCO_wdt: Various improvements

Various coccinelle driven transformations as detailed below.

The conversion was done automatically with coccinelle using the
following semantic patches. The semantic patches and the scripts
used to generate this commit log are available at
https://github.com/groeck/coccinelle-patches



- Use watchdog_stop_on_unregister to stop the watchdog on remove
- Drop assignments to otherwise unused variables
- Drop empty remove function

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>