linux_4_9: remove

Support will be dropped on 01 Jan 2023[1]. Normally we'd keep it around
until then, but considering that it's an LTS kernel it may be better to
do it before 22.11 to make sure there are no unpleasant surprises.

Closes #199933

[1] https://endoflife.date/linux

nixos/doc/manual/from_md/release-notes/rl-2211.section.xml

@@ -861,6 +861,12 @@
           for <literal>termonad</literal> has been removed.
         </para>
       </listitem>
+      <listitem>
+        <para>
+          Linux 4.9 has been removed because it will reach its end of
+          life within the lifespan of 22.11.
+        </para>
+      </listitem>
       <listitem>
         <para>
           (Neo)Vim can not be configured with

nixos/doc/manual/release-notes/rl-2211.section.md

@@ -265,6 +265,8 @@ Available as [services.patroni](options.html#opt-services.patroni.enable).
 
 - The top-level `termonad-with-packages` alias for `termonad` has been removed.
 
+- Linux 4.9 has been removed because it will reach its end of life within the lifespan of 22.11.
+
 - (Neo)Vim can not be configured with `configure.pathogen` anymore to reduce maintainance burden.
   Use `configure.packages` instead.
 - Neovim can not be configured with plug anymore (still works for vim).