events: avoid emit() eager deopt

This commit makes sure EventEmitter.emit() doesn't get deoptimized by
V8. The deopt happens when accessing out of bound indexes of the
`arguments` object.

This issue has been raised here: #10323 and this specific case might
become a more serious performance issue in upcoming V8 releases.

PR-URL: https://github.com/nodejs/node/pull/10568


Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>