USWDS-Site: Remove legacy UA Google tracking code

[amycole501]

The legacy Universal Analytics (UA) tracking code is no longer collecting data. Google recommends removing it. Dan approved removing it

https://designsystem.digital.gov/

This should make a slight improvement on our site speed by removing unused JS.

This is the code to be removed from the header:

<!-- UA -->
--
  | <script>
  | window.ga=window.ga\|\|function(){(ga.q=ga.q\|\|[]).push(arguments)};ga.l=+new Date;
  | ga('create', 'UA-48605964-43', 'gsa.gov');
  | ga('send', 'pageview');
  | // anonymize user IPs (chops off the last IP triplet)
  | ga('set', 'anonymizeIp', true);
  |  
  | // forces SSL even if the page were somehow loaded over http://
  | ga('set', 'forceSSL', true);
  |  
  | ga('send', 'pageview');
  | </script>
  | <script async src='https://www.google-analytics.com/analytics.js'></script>

[amycole501]

Confirmed with analytics experts at GSA that this code is OK to remove from the site.