Remove .html extension from links

chrome/common/extensions/docs/templates/intros/wallpaper.html

 <h2 id="manifest">Manifest</h2>
 <p>You must declare the "wallpaper" permission in the app
-<a href="manifest.html">manifest</a> to use the wallpaper API.
+<a href="manifest">manifest</a> to use the wallpaper API.
 For example:</p>
 <pre data-filename="manifest.json">
 {
   "name": "My extension",
   ...
   <b>"permissions": [
     "wallpaper"
   ]</b>,
   ...
 }</pre>
 
 <h2 id="overview-examples">Examples</h2>
 
 <p>
 For example, to set the wallpaper as the image at
 <code>http://example.com/a_file.png</code>, you can call
 <code>chrome.wallpaper.setWallpaper</code> this way:
 </p>
 
 <pre>
 chrome.wallpaper.setWallpaper(
     {
       'url': 'http://example.com/a_file.jpg',
       'layout': 'CENTER_CROPPED',
       'name': 'test_wallpaper'
     }, function() {});
 </pre>