方法说明：

移除指定事件的某个监听器。

语法：

emitter.removeListener(event, listener)

接收参数：

event (string) 事件类型

listener (function) 已注册过的监听器

例子：

var callback = function(stream) {

  console.log('someone connected!');

};

server.on('connection', callback);

// ...

server.removeListener('connection', callback);

源码：

// emits a 'removeListener' event iff the listener was removed

EventEmitter.prototype.removeListener = function(type, listener) {

  var list, position, length, i;

  if (!util.isFunction(listener))

    throw TypeError('listener must be a function');

  if (!this._events || !this._events[type])

    return this;

  list = this._events[type];

  length = list.length;

  position = -1;

  if (list === listener ||

      (util.isFunction(list.listener) && list.listener === listener)) {

    delete this._events[type];

    if (this._events.removeListener)

      this.emit('removeListener', type, listener);

  } else if (util.isObject(list)) {

    for (i = length; i-- > 0;) {

      if (list[i] === listener ||

          (list[i].listener && list[i].listener === listener)) {

        position = i;

        break;

      }

    }

    if (position < 0)

      return this;

    if (list.length === 1) {

      list.length = 0;

      delete this._events[type];

    } else {

      list.splice(position, 1);

    }

    if (this._events.removeListener)

      this.emit('removeListener', type, listener);

  }

  return this;

};