BUG 865: Deprecate yang-model-util InstanceIdentifier

Users should use its yang-data-api counterpart instead.

Change-Id: I733b4536270c066059f74c775ae6a1a19094127b
Signed-off-by: Robert Varga <rovarga@cisco.com>
(cherry picked from commit 3c42d51a0186c8cd71461d7ba05ca2ef6ba1bf9b)