ath79: sysupgrade: remove obsolete sysupgrade watchdog kill

The watchdog kill command was meant for busybox watchdog. Busybox watchdog
was replaced by the procd watchdog mid 2013 with commit df7ce9301a
("busybox: disable the watchdog utility by default"), which makes the kill
command obsolete since quite some time.

Signed-off-by: Mathias Kresin <dev@kresin.me>

target/linux/ath79/base-files/lib/upgrade/platform.sh

@@ -212,13 +212,3 @@ platform_do_upgrade() {
 		;;
 	esac
 }
-
-disable_watchdog() {
-	killall watchdog
-	( ps | grep -v 'grep' | grep '/dev/watchdog' ) && {
-		echo 'Could not disable watchdog'
-		return 1
-	}
-}
-
-append sysupgrade_pre_upgrade disable_watchdog