tests: refactor inclusion of jquery and sendkeys via script tags

Readability is increased by explicitly checking if jquery/sendkeys was
already loaded before evaluating it in the context of ace_inner and the
enclosing container (pad.html). Note that sendkeys is no longer
evaluated in the context of ace_outer, as this isn't needed

Also removes some IE 8/9 legacy code

src/tests/frontend/runner.js

@@ -314,7 +314,6 @@ $(() => (async () => {
   }
   $progressArea.remove();
 
-  await helper.init();
   const grep = getURLParameter('grep');
   if (grep != null) {
     mocha.grep(grep);