readline: refactor construct Interface

Remove the dependency on the arguments.length.

PR-URL: https://github.com/nodejs/node/pull/4740


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>