DcTracker registers listener for multiple times.

When new sub info records are added, the SubscriptionController will
update all DcTrackers. The DcTracker registers listeners in its update()
method. If the update() method is called multiple times, the listener
will be registered for multiple times too.

Bug: 27953753
Change-Id: I66b947236f40135c45151f0f713dc88959392c48