Creating a stream from an EventEmitter should remove listener on destruction

[jgrund]

Consider:

const ee = new EventEmitter();
const s = highland('someEvent', ee);

typeof ee._events.someEvent; // function

s.destroy();

typeof ee._events.someEvent; // function

Given that highland adds a new listener to ee on creation it should also remove that listener on destruction.

We should be able to use _destructors to register the removal:

  function eeHandler () {
    var ctx = mapper.apply(this, arguments);
    self.write(ctx);
  }

  ee.on(xs, eeHandler);

  var removeMethod = ee['removeListener'] || ee['unbind'];

  if (removeMethod)
     this._destructors.push(function () {
       ee[removeMethod](xs, eeHandler);
    });

[vqvu]

Closing since it's been fixed. Fix should be live in 2.10.5 or 3.0.0-beta.4.