BUG-994: Use SchemaPath.getParent()

Now that SchemaPath defines the proper utility method, use it instead of
brewing our own.

Change-Id: If3661c78491ab97e70627dfffcd902a21bd93e83
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-994: Use SchemaPath.getParent()"