Remove firebug comments

Firebug is discontinued and it's features are included in browser
development tools now a days.

tests/vnc_playback.html

@@ -30,10 +30,5 @@
 
     </body>
 
-    <!--
-    <script type='text/javascript'
-        src='http://getfirebug.com/releases/lite/1.2/firebug-lite-compressed.js'></script>
-    -->
-
     <script type="module" src="./playback-ui.js">
 </html>

vnc.html

@@ -56,11 +56,6 @@
     <!-- Stylesheets -->
     <link rel="stylesheet" href="app/styles/base.css" />
 
-    <!--
-    <script type='text/javascript'
-        src='http://getfirebug.com/releases/lite/1.2/firebug-lite-compressed.js'></script>
-    -->
-
     <!-- this is included as a normal file in order to catch script-loading errors as well -->
     <script type="text/javascript" src="app/error-handler.js"></script>
 

vnc_lite.html

@@ -55,11 +55,6 @@
     <!-- Stylesheets -->
     <link rel="stylesheet" href="app/styles/lite.css">
 
-     <!--
-    <script type='text/javascript'
-        src='http://getfirebug.com/releases/lite/1.2/firebug-lite-compressed.js'></script>
-    -->
-
     <!-- promise polyfills promises for IE11 -->
     <script src="vendor/promise.js"></script>
     <!-- ES2015/ES6 modules polyfill -->