screens: Remove explicit Screen constructors

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

src/displayapp/screens/Motion.cpp

@@ -6,7 +6,7 @@
 using namespace Pinetime::Applications::Screens;
 
 Motion::Motion(Pinetime::Applications::DisplayApp* app, Controllers::MotionController& motionController)
-  : Screen(app), motionController {motionController} {
+  : motionController {motionController} {
   chart = lv_chart_create(lv_scr_act(), nullptr);
   lv_obj_set_size(chart, 240, 240);
   lv_obj_align(chart, nullptr, LV_ALIGN_IN_TOP_MID, 0, 0);