Listeners incorrectly removed

[lpinca]

Ultron removes listeners not added with Ultron when the listener is the same.

const EventEmitter = require('events');
const assert = require('assert');
const Ultron = require('.');

function listener() {}

const ee = new EventEmitter();
const ultron = new Ultron(ee);

ee.on('foo', listener);
ultron.on('foo', listener);

ultron.remove('foo');

assert.strictEqual(ee.listenerCount('foo'), 1);

The issue has been indirectly reported by @apapirovski in nodejs/node#17440 (comment).

[lpinca]

I think that using Ultron to add an already existing listener on an event emitter or using the event emitter to add a listener already added with Ultron doesn't make much sense so this is probably an edge case, but still valid.

[Horaddrim]

I think it's valid, I can PR this if you guys think it's cool! 😄

[lpinca]

Yes, fixing this would be nice.