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/Client.cpp b/services/surfaceflinger/Client.cpp
index b0f2330..c28254f 100644
--- a/services/surfaceflinger/Client.cpp
+++ b/services/surfaceflinger/Client.cpp
@@ -140,9 +140,8 @@
         }
         sp<ISurface> getResult() const { return result; }
         virtual bool handler() {
-            // TODO don't require display id to create a layer
             result = flinger->createLayer(params, name, client,
-                    ISurfaceComposer::eDisplayIdMain, w, h, format, flags);
+                    w, h, format, flags);
             return true;
         }
     };