image.mk: remove obsolete SUBTARGETS variable

Signed-off-by: Felix Fietkau <[email protected]>

include/image.mk

@@ -436,7 +436,6 @@ endef
 
 define Device/Init
   PROFILES := $(PROFILE)
-  SUBTARGETS := $(SUBTARGET)
   DEVICE_NAME := $(1)
   DEVICE_TITLE :=
   DEVICE_PACKAGES :=