public TSStatus pollRegionMaintainTask() {
    synchronized (regionMaintainTaskList) {
      regionMaintainTaskList.remove(0);
      return RpcUtils.SUCCESS_STATUS;
    }
  }
Poll the head of RegionMaintainTasks from the regionMaintainTaskList after it's executed
successfully.

@return {@link TSStatusCode#SUCCESS_STATUS}
iotdb-core/confignode/src/main/java/org/apache/iotdb/confignode/persistence/partition/PartitionInfo.java