Sunsetting PowerDevil's XRandrBrightness

[Kai Uwe Broulik]

Hi all,

PowerDevil has two (three, if you count DDC) means of controlling screen 
brightness:

* Writing to sysfs (/sys/class/backlight and /sys/class/leds)
* Using XRandr output property

XRandR is doing X calls and we have some lovely animated screen 
brightness change. However, the UPower "backend" in PowerDevil is quite 
a spaghetti class and having multiple ways to control LEDs doesn't help.

Can we get rid of the XRandrBrightness class and just use sysfs in every 
case? XRandR Brightness doesn't work on Wayland, obviously, and the 
Intel driver which supported it is dead. Are there any other GPU drivers 
or models that use XRandR over sysfs? AMD, nvidia? I vaguely recall 
something but I don't know for sure.

(We're super early in the 5.20 cycle, so if we rip it out now, we still 
have four months to ignore any requests to put it back in ;)

Cheers
Kai Uwe