code: public boolean hasPurgeableTombstones(int gcBefore)
    {
      if (topLevel.localDeletionTime < gcBefore)
        return true;
  
      return ranges != null && ranges.hasPurgeableTombstones(gcBefore);
    }
docs: Returns true if {@code purge} would remove the top-level tombstone or any of the range
  tombstones, false otherwise.
  @param gcBefore timestamp (in seconds) before which tombstones should be purged