godoc: remove paragraph tags around navigation div

R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/4551051

lib/godoc/godoc.html

@@ -56,11 +56,9 @@
     <span class="subtitle">{@|html-esc}</span>
   {.end}
 
-  <p>
   <!-- The Table of Contents is automatically inserted in this <div>.
        Do not delete this <div>. -->
   <div id="nav"></div>
-  </p>
 
   <!-- Content is HTML-escaped elsewhere -->
   {Content}