Disable DNS-backed key-value store

I'm disabling the key-value store because no one was using it.

There are other reasons, too:

- The removal of the `etcd` library dropped the executable size by over
  half from 17MB to 7MB
- I didn't want users who've deployed it internally to be "surprised" by
  unexpected key-value features
- Key-value-over-DNS has a seamy side to it: "data exfiltration". I know
  there are legitimate uses for it, but I've come to believe that a
  Key-value-over-HTTP solution is preferable because it's not only more
  legitimate but also because it eliminates the DNS caching problem.

k8s/document_root_k-v.io/index.html

@@ -36,6 +36,8 @@
   <main role="main" class="container">
     <div class="starter-template">
       <h1>k-v.io</h1>
+      <p>k-v.io is under construction. I've dismantled the DNS-backed key-value store—no one was using it. Stay
+      tuned.</p><!--
       <p>A DNS-based Key-Value Store. <a href="https://ci.nono.io/teams/main/pipelines/sslip.io"><img alt="badge" src=
       "https://ci.nono.io/api/v1/teams/main/pipelines/sslip.io/badge"></a></p>
       <h2>Quick Start</h2>
@@ -115,6 +117,8 @@
         </li>
       </ul>
     </div>
+    -->
+    </div>
   </main><!-- /.container -->
   <script src="https://code.jquery.com/jquery-3.3.1.slim.min.js" integrity=
   "sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo" crossorigin="anonymous"></script>