Remove unused require

src/notifications.js

@@ -30,8 +30,7 @@ const assert = require('assert'),
     eventlog = require('./eventlog.js'),
     mailer = require('./mailer.js'),
     settings = require('./settings.js'),
-    users = require('./users.js'),
-    util = require('util');
+    users = require('./users.js');
 
 const NOTIFICATION_FIELDS = [ 'id', 'eventId', 'title', 'message', 'creationTime', 'acknowledged' ];