Security page has outdated info

https://emberjs.com/security/

This page asking for help in #emberjs, which hasn't been around for years. It also says the best way to get security updates is to sign up for [the Ember Security mailing list](https://groups.google.com/g/ember-security), but I can see that hasn't had a post since 2015.

At a minimum these details should be removed. As an Ember consumer it makes me question how much of this page is factual, and how I can ensure I am on top of security vulnerabilities 😬