base-files: remove default /etc/config/network, generate it via board.d instead

package/base-files/files/etc/board.d/99-default_network

package/base-files/files/etc/config/network

target/linux/adm8668/base-files.mk

target/linux/ar71xx/base-files.mk

target/linux/arc770/base-files.mk

target/linux/at91/base-files.mk

target/linux/bcm53xx/base-files.mk

target/linux/brcm2708/base-files.mk

target/linux/brcm47xx/base-files.mk

target/linux/brcm63xx/base-files.mk

target/linux/imx6/base-files.mk

target/linux/ipq806x/base-files.mk

target/linux/kirkwood/base-files.mk

target/linux/lantiq/base-files.mk

target/linux/malta/base-files.mk

target/linux/mediatek/base-files.mk

target/linux/mpc85xx/base-files.mk

target/linux/mvebu/base-files.mk

target/linux/netlogic/base-files.mk

target/linux/octeon/base-files.mk