message: Impliment delete_account_linking
diff: @@ -465,6 +465,13 @@ function Facebookbot(configuration) {
  };
  facebook_botkit.api.thread_settings.postAPI(message);
  },
  + delete_account_linking: function() {
  + var message = {
  + 'setting_type': 'call_to_actions',
  + 'thread_state': 'existing_thread'
  + };
  + facebook_botkit.api.thread_settings.deleteAPI(message);
  + },
  postAPI: function(message) {
  request.post('https://graph.facebook.com/v2.6/me/thread_settings?access_token=' + configuration.access_token,
  {form: message},
  