Remove given application from the configuration file.
The configuration file is written in JSON.

@param {String} app The app name as it's typed by the user (user/repo).
function (app) {
    var ret = false;
    if (config.apps[app] !== undefined) {
      delete config.apps[app];
      configHelpers.saveConfig();
      ret = true;
    }
    return ret;
  }