build: detach apk repository handling from rootfs.mk

To better support imagebuilder declaring --repositories-file on calling
apk macro, detach this and --repository from rootfs.mk macro and move it
to package Makefile and image.mk where they are used to permit a more
generic usage.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>

include/rootfs.mk

@@ -47,12 +47,10 @@ apk = \
   IPKG_INSTROOT=$(1) \
   $(FAKEROOT) $(STAGING_DIR_HOST)/bin/apk \
 	--root $(1) \
-	--repositories-file /dev/zero \
 	--keys-dir $(TOPDIR) \
 	--no-cache \
 	--no-logfile \
-	--preserve-env \
-	--repository file://$(PACKAGE_DIR_ALL)/packages.adb
+	--preserve-env
 
 TARGET_DIR_ORIG := $(TARGET_ROOTFS_DIR)/root.orig-$(BOARD)