Remove commented out code from viewer.html

The line that this patch removes has been commented out since 2012 (!), see commit c8a6a9ba00.

Also, since the patch is trivial, I'm fixing the formatting of a comment to stop [GitHub from marking it with a red color](https://github.com/mozilla/pdf.js/blob/master/web/viewer.html#L394) (and IE from complaining).

web/viewer.html

@@ -239,7 +239,6 @@ http://sourceforge.net/adobe/cmap/wiki/License/
                 <button id="download" class="toolbarButton download hiddenMediumView" title="Download" tabindex="34" data-l10n-id="download">
                   <span data-l10n-id="download_label">Download</span>
                 </button>
-                <!-- <div class="toolbarButtonSpacer"></div> -->
                 <a href="#" id="viewBookmark" class="toolbarButton bookmark hiddenSmallView" title="Current view (copy or open in new window)" tabindex="35" data-l10n-id="bookmark">
                   <span data-l10n-id="bookmark_label">Current View</span>
                 </a>
@@ -391,6 +390,6 @@ http://sourceforge.net/adobe/cmap/wiki/License/
     <div id="printContainer"></div>
 <!--#if !(FIREFOX || MOZCENTRAL)-->
 <!--#include viewer-snippet-mozPrintCallback-polyfill.html-->
-<!--#endif--->
+<!--#endif-->
   </body>
 </html>