[ar71xx] defconfig: remove network config installed by base-files so defconfig can work

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@14664 3c298f89-4303-0410-b956-a3cf2f4a3e73

target/linux/ar71xx/base-files.mk

+define Package/base-files/install-target
+	rm -f $(1)/etc/config/network
+endef
+
+