apalis-tk1: configs: remove legacy usbboot command

Remove obsolete legacy usbboot wrapper, as distroboot can handle
booting from USB drivers.

Signed-off-by: Igor Opaniuk <igor.opaniuk@toradex.com>
Reviewed-by: Oleksandr Suvorov <oleksandr.suvorov@toradex.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>