ARM: IGEP0033: Remove undef of CONFIG_CMD_MEMTEST

After commit:

  79cd2f81 config_cmd_default.h: Remove CONFIG_CMD_MEMTEST

It's not necessary to undef the CONFIG_CMD_MEMTEST, so we can remove it from
configuration file.

Signed-off-by: Enric Balletbo i Serra <eballetbo@iseebcn.com>
Reviewed-by: Javier Martinez Canillas <javier@dowhile0.org>