lantiq: nand: drop ubifs images

Users are confused which image type they should use and there are more
drawbacks than adavantages in using a r/w ubifs rootfs in constrast to
a read-only squashfs rootfs like:

 - less available free flash space due to better compression of squashfs
   images
 - no support for factory reset due to r/w filesystem
 - possibility to break failsafe due to r/w filesystem

Therefore, drop support for r/w ubifs rootfs images.

Signed-off-by: Mathias Kresin <dev@kresin.me>

target/linux/lantiq/xrx200/target.mk

@@ -1,7 +1,7 @@
 ARCH:=mips
 SUBTARGET:=xrx200
 BOARDNAME:=XRX200
-FEATURES:=squashfs atm nand ubifs
+FEATURES:=squashfs atm nand
 CPU_TYPE:=24kc
 
 DEFAULT_PACKAGES+=kmod-leds-gpio \

target/linux/lantiq/xway/target.mk

@@ -1,7 +1,7 @@
 ARCH:=mips
 SUBTARGET:=xway
 BOARDNAME:=XWAY
-FEATURES:=squashfs atm nand ubifs ramdisk
+FEATURES:=squashfs atm nand ramdisk
 CPU_TYPE:=24kc
 
 DEFAULT_PACKAGES+=kmod-leds-gpio kmod-gpio-button-hotplug swconfig