platform/x86: apple-gmux: Stop calling acpi/video.h functions

Now that acpi_video_get_backlight_type() has apple-gmux detection (using
apple_gmux_present()), it is no longer necessary for the apple-gmux code
to manually remove possibly conflicting drivers.

So remove the handling for this from the apple-gmux driver.

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