code: def on_trial_remove(self, trial_runner, trial):
          
          bracket, _ = self._trial_info[trial]
          bracket.cleanup_trial(trial)
          if not bracket.finished():
              self._process_bracket(trial_runner, bracket, trial)
docs: Notification when trial terminates.
  
          Trial info is removed from bracket. Triggers halving if bracket is
          not finished.