Remove deprecated concepts.util.ListenerRegistry

This class has been deprecated for Helium release, now we are removing
it. Users should use org.opendaylight.yangtools.util.ListenerRegistry.

Change-Id: I4b74d7326641f4f5a86437b08e2b2ca34de8d2b5
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "Remove deprecated concepts.util.ListenerRegistry"