refactor(aio): move unused images to `unused` directories

This prevents the ServiceWorker from prefetching unnecessary files.

aio/content/marketing/index.html

@@ -74,7 +74,7 @@
     <!-- Group 3-->
     <div layout="row" layout-xs="column" class="home-row">
       <div class="promo-img-container promo-3">
-        <div><img src="assets/images/home/joyful-development.png" alt="IDE example"></div>
+        <div><img src="assets/images/home/joyful-development.svg" alt="IDE example"></div>
       </div>
 
       <div class="text-container">
@@ -100,7 +100,7 @@
 
       <div class="promo-img-container promo-4">
         <div>
-          <img src="assets/images/home/loved-by-millions.png" alt="angular on the map" width="455" height="228">
+          <img src="assets/images/home/loved-by-millions.svg" alt="angular on the map" width="455" height="228">
         </div>
       </div>
     </div>