Remove a child from a PID concept.

def remove_child(self, child_pid, reorder=False):
        """Remove a child from a PID concept."""
        super(PIDNodeOrdered, self).remove_child(child_pid)
        child_relations = self._resolved_pid.child_relations.filter(
            PIDRelation.relation_type == self.relation_type.id).order_by(
                PIDRelation.index).all()
        if reorder:
            for idx, c in enumerate(child_relations):
                c.index = idx