Remove all occurrences of a species from a molecule.

        Args:
            species: Species to remove.

def remove_species(self, species):
        """
        Remove all occurrences of a species from a molecule.

        Args:
            species: Species to remove.
        """
        new_sites = []
        species = [get_el_sp(sp) for sp in species]
        for site in self._sites:
            new_sp_occu = {sp: amt for sp, amt in site.species.items()
                           if sp not in species}
            if len(new_sp_occu) > 0:
                new_sites.append(Site(new_sp_occu, site.coords,
                                      properties=site.properties))
        self._sites = new_sites