A wrapper for Molecule.remove_sites().

        :param indices: list of indices in the current Molecule (and graph) to
            be removed.
        :return:

def remove_nodes(self, indices):
        """
        A wrapper for Molecule.remove_sites().

        :param indices: list of indices in the current Molecule (and graph) to
            be removed.
        :return:
        """

        self.molecule.remove_sites(indices)
        self.graph.remove_nodes_from(indices)

        mapping = {}
        for correct, current in enumerate(sorted(self.graph.nodes)):
            mapping[current] = correct

        nx.relabel_nodes(self.graph, mapping, copy=False)
        self.set_node_attributes()