ar71xx: remove AP83 reference design board support

This board is very old and unlikely to still be relevant today. Support
for it contains a significant amount of device specific baggage which is
worth getting rid of.

Signed-off-by: Felix Fietkau <nbd@nbd.name>

target/linux/ar71xx/base-files/lib/ar71xx.sh

@@ -468,9 +468,6 @@ ar71xx_board_detect() {
 	*AP81)
 		name="ap81"
 		;;
-	*AP83)
-		name="ap83"
-		;;
 	*AP90Q)
 		name="ap90q"
 		;;

target/linux/ar71xx/base-files/lib/preinit/05_set_preinit_iface_ar71xx

@@ -13,7 +13,6 @@ set_preinit_iface() {
 	ap135-020 |\
 	ap136-020 |\
 	ap147-010 |\
-	ap83 |\
 	archer-c5 |\
 	archer-c7 |\
 	bhr-4grv2 |\

target/linux/ar71xx/base-files/lib/upgrade/platform.sh

@@ -177,7 +177,6 @@ platform_check_image() {
 	airrouter|\
 	ap132|\
 	ap81|\
-	ap83|\
 	ap90q|\
 	bullet-m|\
 	c-55|\