Improve interstitial behavior

Remove if no password during pre-render
Remove if no password during onFrontMatterChanged
Remove self if on production host

src/transforms/optional-components.js

@@ -50,6 +50,8 @@ export default function(dom, data) {
       interstitial.password = data.password;
       body.insertBefore(interstitial, body.firstChild);
     }
+  } else if (!hasPassword && interstitial) {
+    interstitial.parentElement.removeChild(this);
   }
 
   let appendix = dom.querySelector('d-appendix');