Delete references from the index of the key old value(s).

def delete_from_index(self, key):
        "Delete references from the index of the key old value(s)."
        old_value = self.data[key]
        keys = set(old_value.keys()).intersection(self.indexes.keys())
        for index_name in keys:
            if old_value[index_name] in self.indexes[index_name]:
                del self.indexes[index_name][old_value[index_name]]