BUG-994: remove the legacy public constructor

This removes the constructor, so SchemaPaths are impossible to create
directly, allowing us to evolve and optimize the class further.

Change-Id: Id8ced3d26f012be98504aa1c44ebe1d732b288ba
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-994: remove the legacy public constructor"