BUG-865: remove InstanceIdentifier.Builder.getIdentifier()

This method has been long-deprecated, so let's just remove it.

Change-Id: Ib4ab7be5c463729607ae75c10d0ae6c500c5990b
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-865: remove InstanceIdentifier.Builder.getIdentifier()"