[Memory Leak] Fix leak of NexusLauncehrActivity via AbsSwipeUpHandler#mRecentsAnimationStartCallbacks -> SurfaceTransactionApplier

Fix: 397559243
Flag: NONE - released code
Test: presubmit
Change-Id: I8a1a03575e98bdbe44c70f2bd691f6930ac8b8fd
diff --git a/quickstep/src/com/android/quickstep/AbsSwipeUpHandler.java b/quickstep/src/com/android/quickstep/AbsSwipeUpHandler.java
index 3640e1f..67a54e6 100644
--- a/quickstep/src/com/android/quickstep/AbsSwipeUpHandler.java
+++ b/quickstep/src/com/android/quickstep/AbsSwipeUpHandler.java
@@ -223,6 +223,7 @@
         mRecentsView = null;
         mContainer = null;
         mStateCallback.clearState(STATE_LAUNCHER_PRESENT);
+        mRecentsAnimationStartCallbacks.clear();
     };
 
     private static int FLAG_COUNT = 0;