Activity Transitions: Don't do a shared element exit transition twice.

Bug 15671433

Change-Id: I888702df5661c769cc1c093d859fd85e5e33d282
diff --git a/core/java/android/app/ExitTransitionCoordinator.java b/core/java/android/app/ExitTransitionCoordinator.java
index 2dacb10..18a9468 100644
--- a/core/java/android/app/ExitTransitionCoordinator.java
+++ b/core/java/android/app/ExitTransitionCoordinator.java
@@ -226,13 +226,7 @@
     }
 
     private void startExitTransition() {
-        Transition sharedElementTransition = mSharedElements.isEmpty()
-                ? null : getSharedElementTransition();
-        if (sharedElementTransition == null) {
-            sharedElementTransitionComplete();
-        }
-        Transition transition = mergeTransitions(sharedElementTransition,
-                getExitTransition());
+        Transition transition = getExitTransition();
         if (transition != null) {
             TransitionManager.beginDelayedTransition(getDecor(), transition);
             setViewVisibility(mTransitioningViews, View.INVISIBLE);