docs: def _delete_rows(args):
      """Delete the given row keys from the given Bigtable.
  
      The args are (BigtableSpec, row_keys), but are passed
      as a single argument in order to work with
      multiprocessing.Pool.map.  This is also the reason why this is a
      top-level function instead of a method.
  
      """
      btspec, row_keys = args
      bt_table = bigtable.Client(btspec.project).instance(
          btspec.instance).table(btspec.table)
      rows = [bt_table.row(k) for k in row_keys]
      for r in rows:
          r.delete()
      bt_table.mutate_rows(rows)
      return row_keys