code: def delete_attachment(self, file_name, repository_id, pull_request_id, project=None):
          
          route_values = {}
          if project is not None:
              route_values['project'] = self._serialize.url('project', project, 'str')
          if file_name is not None:
              route_values['fileName'] = self._serialize.url('file_name', file_name, 'str')
          if repository_id is not None:
              route_values['repositoryId'] = self._serialize.url('repository_id', repository_id, 'str')
          if pull_request_id is not None:
              route_values['pullRequestId'] = self._serialize.url('pull_request_id', pull_request_id, 'int')
          self._send(http_method='DELETE',
                     location_id='965d9361-878b-413b-a494-45d5b5fd8ab7',
                     version='5.1-preview.1',
                     route_values=route_values)
docs: DeleteAttachment.
          [Preview API] Delete a pull request attachment.
          :param str file_name: The name of the attachment to delete.
          :param str repository_id: The repository ID of the pull request’s target branch.
          :param int pull_request_id: ID of the pull request.
          :param str project: Project ID or project name