removeFromIdIndex_(feature) {
    for (const id in this.idIndex_) {
      if (this.idIndex_[id] === feature) {
        delete this.idIndex_[id];
        break;
      }
    }
  }
Remove a feature from the id index.  Called internally when the feature id
may have changed.
@param {FeatureType} feature The feature.
@private