treewide: drop unused get_status_led functions

The function isn't used for targets getting the status leds from the
devicetree.

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

target/linux/ath79/base-files/etc/diag.sh

@@ -7,10 +7,6 @@ failsafe="$(get_dt_led failsafe)"
 running="$(get_dt_led running)"
 upgrade="$(get_dt_led upgrade)"
 
-get_status_led() {
-	status_led="$boot"
-}
-
 set_state() {
 	status_led="$boot"