Force full screen refresh with a rounder function

When the screen switches, the full screen needs to be refreshed for the
hardware scrolling to work. This was enforced with backgroundLabels, but
is simpler to do with a rounder function.

src/displayapp/screens/List.cpp

@@ -85,12 +85,6 @@ List::List(uint8_t screenID,
       lv_label_set_text_fmt(labelBt, " %s", applications[i].name);
     }
   }
-
-  lv_obj_t* backgroundLabel = lv_label_create(lv_scr_act(), nullptr);
-  lv_label_set_long_mode(backgroundLabel, LV_LABEL_LONG_CROP);
-  lv_obj_set_size(backgroundLabel, LV_HOR_RES, LV_VER_RES);
-  lv_obj_set_pos(backgroundLabel, 0, 0);
-  lv_label_set_text_static(backgroundLabel, "");
 }
 
 List::~List() {