code: def get_querystring(self):
          
          to_remove = self.get_querystring_parameter_to_remove()
          query_string = urlparse(self.request.get_full_path()).query
          query_dict = parse_qs(query_string.encode('utf-8'))
          for arg in to_remove:
              if arg in query_dict:
                  del query_dict[arg]
          clean_query_string = urlencode(query_dict, doseq=True)
          return clean_query_string
docs: Clean existing query string (GET parameters) by removing
          arguments that we don't want to preserve (sort parameter, 'page')