list-packages: remove useless "language" attribute of "script" element

See http://www.w3.org/TR/html5-diff/#changed-attributes for more information.

* build-aux/list-packages.html (insert-js): remove "language" attribute, useless for the
  "script" element.

build-aux/list-packages.scm

@@ -206,7 +206,7 @@ color:#fff;
 (define (insert-js)
   "Return the JavaScript for the list-packages page."
   (format #t
-"<script language=\"javascript\" type=\"text/javascript\">
+"<script type=\"text/javascript\">
 // license: CC0
 function show_hide(idThing)
 {