build: remove duplicate mksercomfw image recipe

Keep the ramips/mt76x8 copy, since it's only required for this target at
the moment.

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

include/image-commands.mk

@@ -131,16 +131,6 @@ define Build/tplink-safeloader
 		$(if $(findstring sysupgrade,$(word 1,$(1))),-S) && mv $@.new $@ || rm -f $@
 endef
 
-define Build/mksercommfw
-	-$(STAGING_DIR_HOST)/bin/mksercommfw \
-		$@ \
-		$(KERNEL_OFFSET) \
-		$(HWID) \
-		$(HWVER) \
-		$(SWVER)
-endef
-
-
 define Build/append-dtb
 	cat $(KDIR)/image-$(firstword $(DEVICE_DTS)).dtb >> $@
 endef