Delete a NApp.

        Raises:
            requests.HTTPError: If 400 <= status < 600.

def delete(self, username, napp):
        """Delete a NApp.

        Raises:
            requests.HTTPError: If 400 <= status < 600.

        """
        api = self._config.get('napps', 'api')
        endpoint = os.path.join(api, 'napps', username, napp, '')
        content = {'token': self._config.get('auth', 'token')}
        response = self.make_request(endpoint, json=content, method='DELETE')
        response.raise_for_status()