code: def destroy_label(self, label, callback=dummy_progress_cb):
          
          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()
docs: Remove the label 'label' from all the documents. Takes care of updating
          the index.