Revert PR #472: Add CSP: upgrade-insecure-requests

This caused the playground to hang.

Author: gkellogg

playground/index.html

@@ -14,7 +14,7 @@
     <!-- Meta Tags -->
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <meta http-equiv="Content-Type" content="text/html;charset=utf-8" />
-    <meta http-equiv="Content-Security-Policy" content="upgrade-insecure-requests">
+
 
     <!-- Style Sheets -->
     <link rel="stylesheet" type="text/css" href="../static/css/bootstrap/bootstrap.css">