'Delete the given event in primary calendar of google cal.
:param event_id : google cal identifier of the event to delete'

def delete_an_event(self, event_id):

    params = {'access_token': self.get_token()}
    headers = {'Content-type': 'application/json', 'Accept': 'text/plain'}
    url = ('/calendar/v3/calendars/%s/events/%s' % ('primary', event_id))
    return self.env['google.service']._do_request(url, params, headers, type='DELETE')
