ACPI video: remove deprecated procfs I/F

Remove the deprecated ACPI video driver procfs I/F,
as stated in the changelog of commit 6e37c658

New sysfs I/F is available at /sys/class/backlight/

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>