async removeFromDRM_(uri, manifestDb, muxer) {
    goog.asserts.assert(this.networkingEngine_, 'Cannot be destroyed');
    await shaka.offline.Storage.deleteLicenseFor_(
        this.networkingEngine_, this.config_.drm, muxer, manifestDb);
  }
@param {!shaka.offline.OfflineUri} uri
@param {shaka.extern.ManifestDB} manifestDb
@param {!shaka.offline.StorageMuxer} muxer
@return {!Promise}
@private