platform/x86: asus-wmi: Drop DMI chassis-type check from backlight handling

Remove this check from the asus-wmi backlight handling:

	/* Some Asus desktop boards export an acpi-video backlight interface,
	   stop this from showing up */
	chassis_type = dmi_get_system_info(DMI_CHASSIS_TYPE);
	if (chassis_type && !strcmp(chassis_type, "3"))
		acpi_video_set_dmi_backlight_type(acpi_backlight_vendor);

This acpi_video_set_dmi_backlight_type(acpi_backlight_vendor) call must be
removed because other changes in this series change the native backlight
drivers to no longer unconditionally register their backlight. Instead
these drivers now do this check:

        if (acpi_video_get_backlight_type(false) != acpi_backlight_native)
                return 0; /* bail */

So leaving this in place can break things on laptops with a broken
DMI chassis-type, which would have GPU native brightness control before
the addition of the acpi_video_get_backlight_type() != native check.

Removing this should be ok now, since the ACPI video code has improved
heuristics for this itself now (which includes a chassis-type check).

Signed-off-by: Hans de Goede <hdegoede@redhat.com>