removeInstance(instancingId, instancedSprite) {
    const instances = this._instancesById[instancingId];
    if (instances != null) {
      const index = _.indexOf(instances, instancedSprite);
      if (index != -1) {
        // remove instance from list
        instances.splice(index, 1);

        // cleanup instance
        this._cleanupInstance(instancedSprite);

        // flag this instancing as dirty
        this.setInstancesDirty(instancingId);
      }
    }
  }
Removes a sprite as an instance.
@param {String} instancingId
@param {cc.Sprite} instancedSprite