Unregister the package event listeners when they are not used.

Bug: 175867467
Change-Id: I60e137732bd2c50097ad5d76e2243ad24f4cf8c7
diff --git a/src/com/android/customization/picker/CustomizationPickerActivity.java b/src/com/android/customization/picker/CustomizationPickerActivity.java
index 7736ee2..45f4cf4 100644
--- a/src/com/android/customization/picker/CustomizationPickerActivity.java
+++ b/src/com/android/customization/picker/CustomizationPickerActivity.java
@@ -396,6 +396,11 @@
     }
 
     @Override
+    public void cleanUp() {
+        mDelegate.cleanUp();
+    }
+
+    @Override
     public void onWallpapersReady() {
 
     }