Use Boilerplate: omit feedback-header to eliminate local/remote diff

Thanks @domenic for pointing out how to do this:
speced/bikeshed#477 (comment)

mediasession.bs

@@ -14,7 +14,7 @@ Abstract: notification areas and on lock screens of mobile devices.
 !Participate: <a href="https://github.com/whatwg/mediasession/issues/new">File an issue</a> (<a href="https://github.com/whatwg/mediasession/issues?state=open">open issues</a>)
 !Participate: <a href="https://wiki.whatwg.org/wiki/IRC">IRC: #whatwg on Freenode</a>
 !Version History: <a href="https://github.com/whatwg/mediasession/commits">https://github.com/whatwg/mediasession/commits</a>
-Boilerplate: omit conformance
+Boilerplate: omit conformance, omit feedback-header
 </pre>
 
 <script src=https://resources.whatwg.org/file-issue.js async></script>

mediasession.html

@@ -69,7 +69,7 @@
   <div class="head">
    <p data-fill-with="logo"><a class="logo" href="https://whatwg.org/"> <img alt="WHATWG" height="100" src="https://resources.whatwg.org/logo-mediasession.svg"> </a> </p>
    <h1 class="p-name no-ref" id="title">Media Session</h1>
-   <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Living Standard — Last Updated <time class="dt-updated" datetime="2015-09-08">8 September 2015</time></span></h2>
+   <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Living Standard — Last Updated <time class="dt-updated" datetime="2015-09-17">17 September 2015</time></span></h2>
    <div data-fill-with="spec-metadata">
     <dl>
      <dt>Participate: