Revert "skip the disabled backlight device"

This reverts commits 86c3548d103ff5966366788220796de629be9230 and
5c0d35ca6caf7bb0a0e9897a1a868e8406f3b112.

Not all raw interfaces have device/enabled under the backlight sysfs
interface. Some examples are nvidia-bl and acpi_video0, they are raw
interfaces but doesn't have device/enabled properties.

Overall we can just return true even if file doesn't exist but then this
code serves no purpose.

BUG: 381114
BUG: 381199

Ackd-by: Kai Uwe Broulik <kde@privat.broulik.de>
CCMAIL: AceLan Kao <acelan@acelan.idv.tw>