The u-boot package has some issues causing its build to fail under certain circumstances. As we don't support the ZyXEL devices it's used for anyways, just don't build it anymore.
@@ -1,2 +1,3 @@
CONFIG_TARGET_ar71xx=y
CONFIG_TARGET_ROOTFS_JFFS2=n
+# CONFIG_PACKAGE_uboot-ar71xx-nbg460n_550n_550nh is not set