Refactoring FlingToDelete

> Moving all fling related logic to FlingToDeleteHelper from DragController
> Removing fling related methods from DragSource and DropTarget
> Moving fling animation logic from DeleteDropTarget to FlingAnimation
> Simplifying DropTargetBar to directly look for all valid drop targets.
  This makes it easier to add new DropTarget in xml.

Change-Id: I7214d2d30c907ab93c80d92d9f9be6dda2d63354

src/com/android/launcher3/DropTarget.java

@@ -16,12 +16,10 @@
 
 package com.android.launcher3;
 
-import com.android.launcher3.dragndrop.DragView;
-
-import android.graphics.PointF;
 import android.graphics.Rect;
 
 import com.android.launcher3.accessibility.DragViewStateAnnouncer;
+import com.android.launcher3.dragndrop.DragView;
 
 /**
  * Interface defining an object that can receive a drag.
@@ -116,13 +114,6 @@ public interface DropTarget {
 
     void onDragExit(DragObject dragObject);
 
-    /**
-     * Handle an object being dropped as a result of flinging to delete and will be called in place
-     * of onDrop().  (This is only called on objects that are set as the DragController's
-     * fling-to-delete target.
-     */
-    void onFlingToDelete(DragObject dragObject, PointF vec);
-
     /**
      * Check if a drop action can occur at, or near, the requested location.
      * This will be called just before onDrop.