Sunsetting PowerDevil's XRandrBrightness

[Kai Uwe Broulik]

 > One thing which this will trip over is, if device supports both XRandr
 > and normal backlight control, then code will prefer to still use the
 > XRandr, so not sure if we can "trust" data.

That's on purpose, since XRandR has the smooth brightness animation, I 
always prefer that one, if possible. :)

 > Can we figure out some stats from e.g. bug reports and logs we have
 > available?

Not sure, maybe. or KUserFeedback :D