Remove copyright notice for icons we no longer use

mutalyzer/website/templates/about.html

@@ -39,11 +39,6 @@ Specifications are given by Peter E.M. Taschner and Johan T. den
 Dunnen.
 </p>
 
-<p>
-Some icons are copyright &copy;
-<a href="http://p.yusukekamiyamane.com/">Yusuke Kamiyamane</a>.
-</p>
-
 <p>
 Since references to WWW-sites are not yet acknowledged as citations,
 please mention