hwcomposer HAL uses "default" service name

The getService() and registerAsService() methods of interface objects
now have default parameters of "default" for the service name. HALs
will not have to use any service name unless they want to register
more than one service.

Test: builds

Bug: 33844934
Change-Id: I3d51429681d834f53dc5f6765e97675eafdceda4
diff --git a/graphics/composer/2.1/default/service.cpp b/graphics/composer/2.1/default/service.cpp
index 656673e..712dac1 100644
--- a/graphics/composer/2.1/default/service.cpp
+++ b/graphics/composer/2.1/default/service.cpp
@@ -39,5 +39,5 @@
         ALOGE("Couldn't set SCHED_FIFO: %d", errno);
     }
 
-    return defaultPassthroughServiceImplementation<IComposer>("hwcomposer");
+    return defaultPassthroughServiceImplementation<IComposer>();
 }