[FIX] website_mail_group: duplicate preventDefault() call (called before onclick already)

Plus it fails because `event` is not defined nor passed there (e.g. in Firefox)

addons/website_mail_group/static/src/js/website_mail_group.snippet.js

@@ -33,7 +33,6 @@
             return;
         },
         on_click: function () {
-            event.preventDefault();
             var self = this;
             var $email = this.$target.find(".js_follow_email");