Eradicate DisplayID.

DisplayDevices are now keyed of the wp<IBinder> the client uses.
DisplayID has now become DisplayType which is just used to identify
physical displays (as opposed to virtual displays such as wifi displays).

Change-Id: I0c5968f2c902dcd699a7e0afacf833ff070c12ea
diff --git a/services/surfaceflinger/EventThread.h b/services/surfaceflinger/EventThread.h
index 20ea34d..c8bb312 100644
--- a/services/surfaceflinger/EventThread.h
+++ b/services/surfaceflinger/EventThread.h
@@ -76,7 +76,7 @@
     void onScreenAcquired();
 
     // called when receiving a vsync event
-    void onVSyncReceived(int display, nsecs_t timestamp);
+    void onVSyncReceived(const wp<IBinder>& display, nsecs_t timestamp);
 
     Vector< sp<EventThread::Connection> > waitForEvent(
             DisplayEventReceiver::Event* event);