lantiq: remove deprecated jffs2_nand configuration

As far as I am aware, amongst the lantiq boards, jffs2_nand was
only used on the BTHOMEHUBV2B. Ubi-related modifications to the
device tree for that board mean that the resulting jffs2 images
no longer work, and are no longer required anyway. So I suggest
removing the related configuration, which this patch does.

If anyone else is using jffs2_nand on a lantiq target please speak
up!

Incidentally, for a jffs2 rootfs partition concatenated to the
kernel image to be recognised and mounted correctly on nand
this patch or something equivalent is required:
http://patchwork.openwrt.org/patch/5110/
It is marked as accepted in patchwork but doesn't seem to have
been committed. As far as I am concerned it too is deprecated.

Signed-off-by: Ben Mulvihill <ben.mulvihill@gmail.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@41312 3c298f89-4303-0410-b956-a3cf2f4a3e73