code: func (s *GroupService) Remove(groupname string, username string) (*Response, error) {
  	apiEndpoint := fmt.Sprintf("/rest/api/2/group/user?groupname=%s&username=%s", groupname, username)
  	req, err := s.client.NewRequest("DELETE", apiEndpoint, nil)
  	if err != nil {
  		return nil, err
  	}
  
  	resp, err := s.client.Do(req, nil)
  	if err != nil {
  		jerr := NewJiraError(resp, err)
  		return resp, jerr
  	}
  
  	return resp, nil
  }
docs: // Remove removes user from group
  //
  // JIRA API docs: https://docs.atlassian.com/jira/REST/cloud/#api/2/group-removeUserFromGroup