Pantheon settings.php URL normalizing code - rewrites www.sitename.com (and othersubdomains.sitename.com) to sitename.com

settings-snippet.php

$primary_domain = 'mountainwest.aaa.com';
$primary_schema = 'http://';
$live_subdomain = 'www.';
$test_subdomain = 'test.';
$live_domain = $live_subdomain . $primary_domain;

if (isset($_SERVER['PANTHEON_ENVIRONMENT']) &&
  $_SERVER['PANTHEON_ENVIRONMENT'] === 'test') {
    $base_url = $primary_schema . $test_subdomain . $primary_domain;
  }

if (isset($_SERVER['PANTHEON_ENVIRONMENT']) &&
  $_SERVER['PANTHEON_ENVIRONMENT'] === 'live') {
  
  if($_SERVER['HTTP_HOST'] == $live_domain) {
    $base_url = $primary_schema . $live_domain;
  }
  else {
    header('HTTP/1.0 301 Moved Permanently'); 
    header('Location: '. $primary_schema . $live_domain . $_SERVER['REQUEST_URI']); 
    exit();
  }
}