FCPClientReferenceImplementation: Put unused variable to use

- subscribedObjectType is the variable.
- Also, make it final, should never be modified.
FCPClientReferenceImplementation: Remove obsolete class

FCPIdentitiesSynchronizationHandler was replaced by
FCPBeginSynchronizationNotificationHandler.
FCPClientReferenceImplementation: Remove obsolete class

FCPTrustsSynchronizationHandler was replaced by
FCPBeginSynchronizationNotificationHandler.