events: update and clarify error message

Update error message that's thrown when no error listeners are attached
to an emitter.

PR-URL: https://github.com/nodejs/node/pull/10387


Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Italo A. Casas <me@italoacasas.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>