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.cpp b/services/surfaceflinger/EventThread.cpp
index a39b7d8..dcda67e 100644
--- a/services/surfaceflinger/EventThread.cpp
+++ b/services/surfaceflinger/EventThread.cpp
@@ -106,7 +106,7 @@
 }
 
 
-void EventThread::onVSyncReceived(int, nsecs_t timestamp) {
+void EventThread::onVSyncReceived(const wp<IBinder>&, nsecs_t timestamp) {
     Mutex::Autolock _l(mLock);
     mVSyncTimestamp = timestamp;
     mVSyncCount++;