docs: def remove_dataset_from_collection(dataset_id, collection_id, **kwargs):
      """
          Add a single dataset to a dataset collection.
      """
      collection_i = _get_collection(collection_id)
      collection_item = _get_collection_item(collection_id, dataset_id)
      if collection_item is None:
          raise HydraError("Dataset %s is not in collection %s.",
                                                      dataset_id,
                                                      collection_id)
      db.DBSession.delete(collection_item)
      db.DBSession.flush()
  
      db.DBSession.expunge_all()
  
      return 'OK'