Remove backup brightness feature (#1180)

This feature is not needed and is probably more likely to cause issues. It's better to just use brightnessController.Set(settingsController.GetBrightness());

src/components/brightness/BrightnessController.cpp

@@ -74,14 +74,6 @@ BrightnessController::Levels BrightnessController::Level() const {
   return level;
 }
 
-void BrightnessController::Backup() {
-  backupLevel = level;
-}
-
-void BrightnessController::Restore() {
-  Set(backupLevel);
-}
-
 void BrightnessController::Step() {
   switch (level) {
     case Levels::Low:
@@ -123,4 +115,4 @@ const char* BrightnessController::ToString() {
     default:
       return "???";
   }
-}
+}

src/components/brightness/BrightnessController.h

@@ -15,15 +15,11 @@ namespace Pinetime {
       void Higher();
       void Step();
 
-      void Backup();
-      void Restore();
-
       const char* GetIcon();
       const char* ToString();
 
     private:
       Levels level = Levels::High;
-      Levels backupLevel = Levels::High;
     };
   }
 }