Revert "Remove noVNC sound"

This reverts commit 008c1df7.

The change is redundant, because there is a query parameter which
disabled the sound.

novnc/vnc.html

@@ -336,10 +336,8 @@
             mozactionhint="Enter" tabindex="-1"></textarea>
     </div>
     <audio id="noVNC_bell">
-        <!--
         <source src="app/sounds/bell.oga" type="audio/ogg">
         <source src="app/sounds/bell.mp3" type="audio/mpeg">
-        -->
     </audio>
  </body>
 </html>