board: developerbox: remove obsolete NOR flash layout definition

There are two kinds of NOR flash layout for the Developerbox.
Capsule update for the old layout is no longer available since
it has small capacity for secure world images and can not
house the TA such as fTPM.
This commit removes the definition related to the obsolete
NOR flash layout for the UEFI capsule update.

Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
Acked-by: Jassi Brar <jaswinder.singh@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>