ath79: remove duplicate sysupgrade.bin for dlink_dap-2xxx

sysupgrade.bin has been added to IMAGES twice, resulting in
warnings like:

Makefile:86: warning: overriding recipe for target
  '[...]/tmp/openwrt-ath79-generic-dlink_dap-2660-a1-squashfs-sysupgrade.bin'
Makefile:86: warning: ignoring old recipe for target
  '[...]/tmp/openwrt-ath79-generic-dlink_dap-2660-a1-squashfs-sysupgrade.bin'

Signed-off-by: Adrian Schmutzler <[email protected]>

target/linux/ath79/image/generic.mk

@@ -740,7 +740,7 @@ endef
 TARGET_DEVICES += dlink_dap-1365-a1
 
 define Device/dlink_dap-2xxx
-  IMAGES += factory.img sysupgrade.bin
+  IMAGES += factory.img
   IMAGE/factory.img := append-kernel | pad-offset 6144k 160 | \
 	append-rootfs | wrgg-pad-rootfs | mkwrggimg | check-size
   IMAGE/sysupgrade.bin := append-kernel | mkwrggimg | \