docs: @Override
      public synchronized void remove() {
          verifyAccess();
  //        if (isRemoved()) return; //Remove() is idempotent
          Iterator<TitanRelation> iter = it().query().noPartitionRestriction().relations().iterator();
          while (iter.hasNext()) {
              iter.next();
              iter.remove();
          }
          //Remove all system types on the vertex
          for (TitanRelation r : it().query().noPartitionRestriction().system().relations()) {
              RelationType t = r.getType();
              r.remove();
          }
      }