Simplify DelayedListenerRegistration functionality

Simplify DelayedListenerRegistration functionality

The DelayedListenerRegistration class is abstract with
parameterized sub-classes for the 2 listener types which
don't provide any additional functionality. Consequently
AbstractDataListenerSupport is parameterized with the
DelayedListenerRegistration type with an abstract method
to instantiate the appropriate type.

We can simplify AbstractDataListenerSupport by removing the
type parameter and the abstract method and consequently remove
the 2 DelayedListenerRegistration sub-classes.

Change-Id: I04933753b59748a09c31e0ec5ed4de9666fea364
Signed-off-by: Tom Pantelis <tompantelis@gmail.com>