Kirkwood: NAS220: remove bootdelay from CONFIG_EXTRA_ENV_SETTINGS

The default bootdelay of 3 seconds is good enough and there is no need
to duplicate it in CONFIG_EXTRA_ENV_SETTINGS.

Signed-off-by: Evgeni Dobrev <evgeni@studio-punkt.com>
Signed-off-by: Stefan Roese <sr@denx.de>