Drop references to CDNJS

CDNJS isn't updating correctly and maintenance of that mirror's config
is nearly impossible.

Also adds a reference to jsDelivr in the README, matching what's in
the demo app.

Closes #2343

Backported to v2.5.x

Change-Id: I3a337ccd55ebc4c193ab205a7f8c8a77c33a4b4b

README.md

@@ -168,8 +168,8 @@ attributes.
 
  * [development roadmap](roadmap.md)
  * [hosted demo](http://shaka-player-demo.appspot.com) (sources in `demo/`)
- * [hosted builds on cdnjs](https://cdnjs.com/libraries/shaka-player)
  * [hosted builds on Google Hosted Libraries](https://developers.google.com/speed/libraries/#shaka-player)
+ * [hosted builds on jsDelivr](https://www.jsdelivr.com/package/npm/shaka-player)
  * [announcement list](https://groups.google.com/forum/#!forum/shaka-player-users)
      ([join](docs/announcement-list-join-group.png) for release and survey
       announcements)

demo/index.html

@@ -144,7 +144,6 @@ <h1 class="mdl-mega-footer__heading">CDN</h1>
               <ul class="mdl-mega-footer__link-list">
                 <li><a rel="noopener" target="_blank" href="https://developers.google.com/speed/libraries/#shaka-player">Google Hosted Libraries</a></li>
                 <li><a rel="noopener" target="_blank" href="https://www.jsdelivr.com/package/npm/shaka-player">jsDelivr</a></li>
-                <li><a rel="noopener" target="_blank" href="https://cdnjs.com/libraries/shaka-player">CDNJS</a></li>
               </ul>
             </div>
             <div class="mdl-mega-footer__drop-down-section">