apalis/colibri-imx8/8x: remove global variable script

apalis/colibri-imx8/8x: remove global variable script

The distroboot script system scans boot_scripts variable and
try to find and use to boot each script name mentioned there.
Setting global variable "script" breaks this general mechanism
of searching and running a distro boot script.
Remove global variables "script" to fix working the general
distro boot script mechanism.

Signed-off-by: Oleksandr Suvorov <oleksandr.suvorov@toradex.com>
Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Reviewed-by: Fabio Estevam <festevam@denx.de>