removeBuyNodes(duration) {
    if (this.buyNode != null) {
      if (duration == null) { duration = 0.0; }
      this.removeInteractiveElement(this.buyNode);
      this.buyNode.destroy(duration);
      this.buyNode = null;
    }
  }
Removes current buy node(s).
@param {Number} [duration=0.0] time in seconds