doc: clarify error handling in net.createServer

Remove indications that an error argument is sent to the `listen()` callback.

Fixes: https://github.com/nodejs/node/issues/5345
PR-URL: https://github.com/nodejs/node/pull/5353


Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>