code: func (t *Transaction) deleteStringIndex(collectionName, modelID, fieldName string) {
  	t.Script(deleteStringIndexScript, redis.Args{collectionName, modelID, fieldName}, nil)
  }
docs: // deleteStringIndex is a small function wrapper around a Lua script. The script
  // will atomically remove the existing string index, if any, on the given
  // fieldName for the model with the given modelID. You can use the Name method
  // of a Collection to get its name. fieldName should be the name as it is stored
  // in Redis.