Fix reference count problem as suggested by Ingo.

During DefaultNotificationService's constructor, we get registered
with the NotificationManager, which acquires a reference. When
uninitializing the module we need to release this reference before
calling the destructor in order to balance the books, as it were.
Revert part of previous commit.

The aforementioned ReleaseReference() exposes what appears to be a somewhat
more severe issue, leading us to a deadlock. Need to rethink this a bit.