They are useless, as the platform already selects the right options for
NAND support. The main reason for removing them is the fact that it
makes kernel configs more annoying to maintain on platforms that provide
NAND drivers but disable them (e.g. ramips)

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@45919 3c298f89-4303-0410-b956-a3cf2f4a3e73