Fix leakage of GestureExclusionListener

So the unregister/register are paired when launcher activity
is relaunched:

Launcher#onDestroy
 > mSplitWithKeyboardShortcutController.onDestroy()
+ > RecentsAnimationDeviceState#destroy
+  > unregisterExclusionListener

Launcher#onCreate
 > setupViews
  > new SplitWithKeyboardShortcutController
   > new RecentsAnimationDeviceState
    > onDisplayInfoChanged
     > registerExclusionListener

Bug: 319133753
Test: Toggle screen resolution many times and check the amount
      of DisplayContent#mSystemGestureExclusionListeners.
Change-Id: I2fb84415db71aaa14e653fea2592d6b9b5adad59