code: def drop_index(self, field_name):
      logger.info("Drop index: %s" % self._collection_name)
      return self._milvus.drop_index(self._collection_name, field_name)
  
imports: import random
  import logging
  import time
  from multiprocessing import Process
  from pymilvus import Milvus, DataType
  import utils
  import config
  from milvus_benchmark.runners import utils
label_desc: Use image node_id 20 for calling the MilvusClient obj's underlying member method code with example usage: obj.drop_index(field_name) and returns: self