code: func (material *Material) DeleteMaterial(mediaID string) error {
  	accessToken, err := material.GetAccessToken()
  	if err != nil {
  		return err
  	}
  
  	uri := fmt.Sprintf("%s?access_token=%s", delMaterialURL, accessToken)
  	response, err := util.PostJSON(uri, reqDeleteMaterial{mediaID})
  	if err != nil {
  		return err
  	}
  
  	return util.DecodeWithCommonError(response, "DeleteMaterial")
  }
docs: //DeleteMaterial 删除永久素材