Remove "Using Perl 6" book from newbie list

Until we have unbitrotted this effort, it should probably not be mentioned
to Perl 6 newbies, as it gives a *very* bad impression.

source/documentation/index.html

@@ -33,7 +33,6 @@ <h3>For Newcomers</h3>
             <a href="http://perl6advent.wordpress.com/2010/12/25/merry-christmas-2/">2010</a>,
             <a href="http://perl6advent.wordpress.com/2009/12/01/perl-6-advent-calendar/">2009</a>.
         </li>
-        <li><a href="http://github.com/perl6/book">Using Perl&nbsp;6</a> an open-source Onyx Neon Press book (in progress)</a></li>
 	    <li><a href="http://en.wikibooks.org/wiki/Perl_6_Programming">"Perl&nbsp;6 Programming"</a> on Wikibooks</li>
 	    <li><a href="http://github.com/perlpilot/perl6-docs">Perl&nbsp;6 tutorials</a></li>
 	</ul>