mb/google/beltino: drop ACPI brightness control stub

beltino variants are Chromeboxes without built-in displays,
so now that default_brightness_levels.asl is no longer required
for all boards in a platform, drop it.

Change-Id: Ie8147763fc9fdf4f184d3d000bffd6794e134d9e
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/39946
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/mainboard/google/beltino/dsdt.asl

@@ -38,8 +38,6 @@ DefinitionBlock(
 		{
 			#include <northbridge/intel/haswell/acpi/haswell.asl>
 			#include <southbridge/intel/lynxpoint/acpi/pch.asl>
-
-			#include <drivers/intel/gma/acpi/default_brightness_levels.asl>
 		}
 	}