Remove custom GA Tags script. Use built in GA. (#2794)

Signed-off-by: Steve Richards <srichards@mirantis.com>

docs/custom_theme/main.html

@@ -1,12 +1 @@
 {% extends "base.html" %}
-
-{% block analytics %}
-  <!-- Global site tag (gtag.js) - Google Analytics -->
-  <script async src="https://www.googletagmanager.com/gtag/js?id=G-90E1JB4HW4"></script>
-  <script>
-    window.dataLayer = window.dataLayer || [];
-    function gtag(){dataLayer.push(arguments);}
-    gtag('js', new Date());
-    gtag('config', 'G-90E1JB4HW4');
-  </script>
-{% endblock %}