Refactoring ItemInfo

> Changing dragObject to ItemInfo
> Removing dropPos which is always null
> Removing requiresDbUpdate which is only used in CellLayout

Change-Id: I753ddaae0880c8a9bfee5a1266095ff34610284a

src/com/android/launcher3/SearchDropTargetBar.java

@@ -196,7 +196,7 @@ public class SearchDropTargetBar extends FrameLayout implements DragController.D
      * DragController.DragListener implementation
      */
     @Override
-    public void onDragStart(DragSource source, Object info, int dragAction) {
+    public void onDragStart(DragSource source, ItemInfo info, int dragAction) {
         showDeleteTarget();
     }