ath79: remove SUPPORTED_DEVICES for TP-Link Archer D50 v1

This device has not been supported in ar71xx, so there is no need
for an explicit SUPPORTED_DEVICES entry.
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/ath79/image/generic-tp-link.mk

@@ -271,7 +271,6 @@ define Device/tplink_archer-d50-v1
   IMAGES := sysupgrade.bin
   IMAGE/sysupgrade.bin := tplink-v2-image -s -V "ver. 2.0" | \
         append-metadata | check-size $$$$(IMAGE_SIZE)
-  SUPPORTED_DEVICES += archer-d50-v1
 endef
 TARGET_DEVICES += tplink_archer-d50-v1