Remove unused pointer to DisplayApp member variables (#2125)

In the screens that use `DisplayApp *app` and pass it to a child item,
or use the reference just in the constructor. Afterwards the `app`
member is not used. So remove it from the private member variables.

Completely remove `app` parameter from `SettingDisplay` constructor as
it is unused.

src/displayapp/DisplayApp.cpp

@@ -582,7 +582,7 @@ void DisplayApp::LoadScreen(Apps app, DisplayApp::FullRefreshDirections directio
       currentScreen = std::make_unique<Screens::SettingWakeUp>(settingsController);
       break;
     case Apps::SettingDisplay:
-      currentScreen = std::make_unique<Screens::SettingDisplay>(this, settingsController);
+      currentScreen = std::make_unique<Screens::SettingDisplay>(settingsController);
       break;
     case Apps::SettingSteps:
       currentScreen = std::make_unique<Screens::SettingSteps>(settingsController);