docstr: sort kpts and remove the repeated ones.
code: def _sort_and_unique_bboxes(self, kpts, key="bbox_id"):
      """sort kpts and remove the repeated ones."""
      kpts = sorted(kpts, key=lambda x: x[key])
      num = len(kpts)
      for i in range(num - 1, 0, -1):
          if kpts[i][key] == kpts[i - 1][key]:
              del kpts[i]
  
      return kpts
  
imports: import os
  import json
  from collections import defaultdict, OrderedDict
  import numpy
  import paddle
  from pycocotools.coco import COCO
  from pycocotools.cocoeval import COCOeval
  from ..modeling.keypoint_utils import oks_nms, keypoint_pck_accuracy, keypoint_auc, keypoint_epe
  from scipy.io import loadmat, savemat
  from ppdet.utils.logger import setup_logger
label_desc: Use image node_id 9 for calling the KeyPointTopDownMPIIEval obj's underlying member method code with example usage: obj._sort_and_unique_bboxes(kpts, key) and returns: kpts