code: private void removeTracker(TaskTracker tracker) {
      String trackerName = tracker.getTrackerName();
      // Remove completely after marking the tasks as 'KILLED'
      lostTaskTracker(tracker);
      TaskTrackerStatus status = tracker.getStatus();
  
      // tracker is lost, and if it is blacklisted, remove
      // it from the count of blacklisted trackers in the cluster
      if (isBlacklisted(trackerName)) {
       faultyTrackers.decrBlackListedTrackers(1);
      }
      updateTaskTrackerStatus(trackerName, null);
      statistics.taskTrackerRemoved(trackerName);
      getInstrumentation().decTrackers(1);
    }
docs: Remove a tracker from the system