_content/doc: copypaste.js included more than once

The copypaste js script is included twice, once in the site.tmpl and a
second time in install.html.

_content/doc/install.html

@@ -219,4 +219,3 @@
 
 <script async src="/doc/download.js"></script>
 <script async src="/doc/hats.js"></script>
-<script async src="/js/copypaste.js"></script>