UBUNTU: [Config] Remove CONFIG_MTD_NAND_OXNAS=m

UBUNTU: [Config] Remove CONFIG_MTD_NAND_OXNAS=m

This driver apparently is only needed for one specific platform.
So "mtd: nand: Add OX820 NAND hardware dependency" removes it from
being available if not compiling for ARCH_OXNAS.

Remove it from config.common.ubuntu (as far as I know none of our
master kernel and derivatives in main git tree supports that hw).

BugLink: https://bugs.launchpad.net/bugs/1691369
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>