build: image: drop unused check-kernel-size recipe

The recipe check-kernel-size is not used in the entire tree. Instead,
we already check the size of the kernel image in Device/Build/kernel
in image.mk via check-size function if KERNEL_SIZE is defined.

Therefore, drop the function. Using it would be redundant anyway.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

include/image-commands.mk

@@ -275,13 +275,6 @@ define Build/check-size
 	}
 endef
 
-define Build/check-kernel-size
-	@[ $$(($(subst k,* 1024,$(subst m, * 1024k,$(1))))) -ge "$$(stat -c%s $(IMAGE_KERNEL))" ] || { \
-		echo "WARNING: Kernel for $@ is too big > $(1)" >&2; \
-		rm -f $@; \
-	}
-endef
-
 define Build/combined-image
 	-sh $(TOPDIR)/scripts/combined-image.sh \
 		"$(IMAGE_KERNEL)" \