screens: Remove explicit Screen constructors

This constructor didn't do anything since DisplayApp reference was
removed from the Screen base class.

src/displayapp/screens/FlashLight.cpp

@@ -17,7 +17,7 @@ namespace {
 FlashLight::FlashLight(Pinetime::Applications::DisplayApp* app,
                        System::SystemTask& systemTask,
                        Controllers::BrightnessController& brightnessController)
-  : Screen(app), systemTask {systemTask}, brightnessController {brightnessController} {
+  : systemTask {systemTask}, brightnessController {brightnessController} {
 
   brightnessController.Set(Controllers::BrightnessController::Levels::Low);