BUG-868: remove deprecated YangInstanceIdentifier methods

This cleans up the methods which were previously deprecated. We still
retain the getPath() and toInstance() -- these will be fixed up.

Change-Id: I37b869af069de256484b833608b082cb6edfb15a
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-868: remove deprecated YangInstanceIdentifier methods"