Sending interaction end event at the end of a drag.

1. In explore-by-touch when the user slides two fingers in the same
   direction we consider it a drag gesture. We merge the pointers into
   one and deliver a touch event. When one of the pointers goes up
   we were transitioning into touch exploring state. This means that
   were transitioning to another state in the middle of a gesture which
   creates complications and leads for interaction end event not being
   sent.

   This change transitions out of dragging state when all pointers go up
   - simple and all events are properly sent. Consequentially, staring a
   drag the user has to lift all pointers to touch explore. Since usually
   users either drags or touch explores this seems the simplest and
   *least risky* fix.

bug:7253731

Change-Id: Ie8588fbe9b26cb81312bd7fd377c94732e41e3f8

Author: sganov

services/java/com/android/server/accessibility/TouchExplorer.java

@@ -700,13 +700,6 @@ private void handleMotionEventStateDragging(MotionEvent event, int policyFlags)
                     }
                 }
             } break;
-            case MotionEvent.ACTION_POINTER_UP: {
-                final int pointerId = event.getPointerId(event.getActionIndex());
-                if (mReceivedPointerTracker.isActiveOrWasLastActiveUpPointer(pointerId)) {
-                    sendUpForInjectedDownPointers(event, policyFlags);
-                    mCurrentState = STATE_TOUCH_EXPLORING;
-                }
-             } break;
             case MotionEvent.ACTION_UP: {
                 // Announce the end of a new touch interaction.
                 sendAccessibilityEvent(