Revert markup change that added p element in hgroup

Changing the spec source markup to use a p element in hgroup will need
to wait until after the spec change lands.

source

@@ -60,7 +60,11 @@
    </hgroup>
    <hgroup w-dev>
     <h1><a href="/dev/" rel=home>HTML: The Living Standard</a></h1>
+    <h2 class="no-num no-toc" id="dev-edition-h2">Edition for Web Developers &mdash; Last Updated <span class="pubdate">[DATE: 01 Jan 1901]</span></h2>
+    <!-- FIXME: once the spec is changed to allow p elements as in hgroup,
+         the h2 above needs to be changed to a p element; like this:
     <p class="no-num no-toc" id="dev-edition-h2">Edition for Web Developers &mdash; Last Updated <span class="pubdate">[DATE: 01 Jan 1901]</span></p>
+    -->
    </hgroup>
    <nav w-nosplit w-nodev w-noreview>
     <!-- Note: be sure to keep an even number of <a>s, for small screens where they appear in two columns. -->