daemon: Move brightness toggle logic into KeyboardBrightnessController
The shared BrightnessLogic::BrightnessInfo
struct had a member
called valueBeforeTogglingOff
, with some associated logic that's
only used by its toggled() function.
ScreenBrightnessController
never wanted anything to do with it,
KeyboardBrightnessController
already has a member to store the exact
same thing. Despite the "generic" API, KeyboardBrightnessController
still had to include a special case for toggling between off and on.
Putting this into shared infrastructure just makes everything more complicated than it should be, so let's make it local to the one or two functions where it actually gets used.