ACPI: video: Remove register_backlight_delay module option and code

Since commit 5aa9d943 ("ACPI: video: Don't enable fallback path for
creating ACPI backlight by default"), the delayed registering of
acpi_video# backlight devices has been disabled by default.

The few bugreports where this option was used as a workaround were all
cases where the GPU driver did not call acpi_video_register_backlight()
and the workaround was to pass video.register_backlight_delay=1.

With the recent "ACPI: video: Make acpi_backlight=video work independent
from GPU driver" changes acpi_backlight=video can be used to achieve
the same result. So there is no need for the register_backlight_delay
option + code anymore.

Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>