Revert "nixos/doc: add 21.11 release notes stub"

This reverts commit 6543c61311.

nixos/doc/manual/from_md/release-notes/rl-2111.section.xml

@@ -1,15 +0,0 @@
-<section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="release-21.11">
-  <title>Release 21.11 (<quote>?</quote>, 2021.11/??)</title>
-  <para>
-    In addition to numerous new and upgraded packages, this release has
-    the following highlights:
-  </para>
-  <itemizedlist spacing="compact">
-    <listitem>
-      <para>
-        Support is planned until the end of April 2022, handing over to
-        22.05.
-      </para>
-    </listitem>
-  </itemizedlist>
-</section>

nixos/doc/manual/release-notes/release-notes.xml

@@ -8,7 +8,6 @@
   This section lists the release notes for each stable version of NixOS and
   current unstable revision.
  </para>
- <xi:include href="../from_md/release-notes/rl-2111.section.xml" />
  <xi:include href="rl-2105.xml" />
  <xi:include href="rl-2009.xml" />
  <xi:include href="rl-2003.xml" />

nixos/doc/manual/release-notes/rl-2111.section.md

@@ -1,5 +0,0 @@
-# Release 21.11 (“?”, 2021.11/??) {#release-21.11}
-
-In addition to numerous new and upgraded packages, this release has the following highlights:
-
-* Support is planned until the end of April 2022, handing over to 22.05.