Remove XRandRBrightness
We have animated brightness changes on sysfs these days. Most drivers don't support XRandR brightness these days and it naturally doesn't work on Wayland.
If only we had a KUserFeedback property for what kind of backlight mechanism people were using :)
Did some non-scientific poll in my blog https://blog.broulik.de/2020/05/sunsetting-xrandr-brightness/ and it turns out XRandR is still being used but some people also told me it uses XRandR but could also have used sysfs.
We're pretty early in the 5.21 cycle so let's just push through with this and see how it goes.