Template files: remove a broken link

This link would be added to documentation websites via the template, but the URL is no longer valid.

As this is a URL on the phpdoc.org website, this may need investigation/fixing instead of the link being removed.

docs/.templates/responsive/layout.html

@@ -101,7 +101,7 @@ <h1 class="phpdocumentor-sidebar__category-header">{{ _('Next topic') }}</h1>
     <script src="https://code.jquery.com/jquery-2.2.4.min.js"></script>
     <script src="https://cdn.jsdelivr.net/gh/google/code-prettify@master/loader/run_prettify.js"></script>
     <script src="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/5.12.0/js/all.min.js" integrity="sha256-0vuk8LXoyrmCjp1f0O300qo1M75ZQyhH9X3J6d+scmk=" crossorigin="anonymous"></script>
-    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/5.12.0/css/all.min.css" integrity="sha256-ybRkN9dBjhcS2qrW1z+hfCxq+1aBdwyQM5wlQoQVt/0=" crossorigin="anonymous" />    <link rel="apple-touch-icon" sizes="72x72" href="http://demo.phpdoc.org/Responsive/img/apple-touch-icon-72x72.png">
+    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/5.12.0/css/all.min.css" integrity="sha256-ybRkN9dBjhcS2qrW1z+hfCxq+1aBdwyQM5wlQoQVt/0=" crossorigin="anonymous" />
     <link rel="apple-touch-icon" sizes="114x114" href="{{ pathto('_static/img/favicon.png', 1) }}">
     {%- block linktags %}
     {%- if hasdoc('about') %}