elk-stack: Add release note about elk-5 stack removal

nixos/doc/manual/release-notes/rl-1909.xml

@@ -428,6 +428,16 @@
      any updates from upstream and depends on outdated Python2-based modules.
     </para>
    </listitem>
+   <listitem>
+    <para>
+     Old unsupported versions (<literal>logstash5</literal>,
+     <literal>kibana5</literal>,
+     <literal>filebeat5</literal>,
+     <literal>heartbeat5</literal>,
+     <literal>metricbeat5</literal>,
+     <literal>packetbeat5</literal>) of the ELK-stack and Elastic beats have been removed.
+    </para>
+   </listitem>
 
   </itemizedlist>
  </section>

pkgs/top-level/all-packages.nix

@@ -2879,7 +2879,6 @@ in
   evemu = callPackage ../tools/system/evemu { };
 
   # The latest version used by elasticsearch, logstash, kibana and the the beats from elastic.
-  elk5Version = "5.6.16";
   elk6Version = "6.7.2";
   elk7Version = "7.0.1";