Remove .html extension from links

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

 <h2 id="manifest">Manifest</h2>
 
 <p>You must declare the "management" permission
-in the <a href="manifest.html">extension manifest</a>
+in the <a href="manifest">extension manifest</a>
 to use the management API.
 For example:</p>
 <pre data-filename="manifest.json">
 {
   "name": "My extension",
   ...
   <b>"permissions": [
     "management"
   ]</b>,
   ...
 }</pre>
 
 <p>
 $(ref:management.getPermissionWarningsByManifest) and
 $(ref:management.uninstallSelf) do not require the management permission
 </p>