documentation: watchdog: remove documentation for ixp2000

The ixp2000 watchdog driver was removed in commit 065e8238 ("watchdog: remove ixp2000 driver")

No need to keep its documentation, so remove it.
Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

Documentation/watchdog/watchdog-parameters.txt

@@ -157,11 +157,6 @@ testmode: Watchdog test mode (1 = no reboot), default=0
 nowayout: Watchdog cannot be stopped once started
 	(default=kernel config parameter)
 -------------------------------------------------
-ixp2000_wdt:
-heartbeat: Watchdog heartbeat in seconds (default 60s)
-nowayout: Watchdog cannot be stopped once started
-	(default=kernel config parameter)
--------------------------------------------------
 ixp4xx_wdt:
 heartbeat: Watchdog heartbeat in seconds (default 60s)
 nowayout: Watchdog cannot be stopped once started