frontend: remove unused method NotifyRetrieved from RegistrationResult

The method was causing a findbug warning by starting with capital letter. 
Since it was not in use, better to remove it than rename.

Change-Id: I53d6e76f4446b9c93a203a966a9576f2a20f1dee
Signed-off-by: Alissa Bonas <abonas@redhat.com>