Brightness improvements

- we dont want to save brightness in settings as it is saved in the
hardware
- fixed a few DDCutil weirdness

Commons/Settings.qml

@@ -188,9 +188,6 @@ Singleton {
       property JsonObject brightness
 
       brightness: JsonObject {
-        property real lastBrightness: 50.0
-        property string lastMethod: "internal"
-        property list<var> monitorBrightness: []
         property int brightnessStep: 5
       }