module: remove unused code in module.js

Remove unnecessary condition in lib/module.js.

Refs: https://github.com/nodejs/node/pull/18593#issuecomment-364927965

PR-URL: https://github.com/nodejs/node/pull/18768


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>