x86: remove defunct etherboot image building code

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

target/linux/x86/image/Makefile

@@ -172,13 +172,6 @@ endif
 
 define Image/BuildKernel
 	$(CP) $(KDIR)/bzImage $(BIN_DIR)/$(IMG_PREFIX)-vmlinuz
-  ifneq ($(CONFIG_X86_ETHERBOOT_IMAGES),)
-	rm -f $(BIN_DIR)/$(IMG_PREFIX)-etherboot
-	$(STAGING_DIR_HOST)/bin/mkelfImage \
-		--append=$(CONFIG_X86_ETHERBOOT_BOOTOPTS) \
-		$(KDIR)/bzImage \
-		$(BIN_DIR)/$(IMG_PREFIX)-etherboot
-  endif
 endef
 
 define Image/Prepare