Remove the label 'label' from all the documents. Takes care of updating
        the index.

def destroy_label(self, label, callback=dummy_progress_cb):
        """
        Remove the label 'label' from all the documents. Takes care of updating
        the index.
        """
        current = 0
        total = self.index.get_nb_docs()
        self.index.start_destroy_label(label)
        while True:
            (op, doc) = self.index.continue_destroy_label()
            if op == 'end':
                break
            callback(current, total, self.LABEL_STEP_DESTROYING, doc)
            current += 1
        self.index.end_destroy_label()