code: func removePartitionInfo(tblInfo *model.TableInfo, partName string) int64 {
  	oldDefs := tblInfo.Partition.Definitions
  	newDefs := make([]model.PartitionDefinition, 0, len(oldDefs)-1)
  	var pid int64
  	for i := 0; i < len(oldDefs); i++ {
  		if !strings.EqualFold(oldDefs[i].Name.L, strings.ToLower(partName)) {
  			continue
  		}
  		pid = oldDefs[i].ID
  		newDefs = append(oldDefs[:i], oldDefs[i+1:]...)
  		break
  	}
  	tblInfo.Partition.Definitions = newDefs
  	return pid
  }
docs: // removePartitionInfo each ddl job deletes a partition.