Update IRC chat https://webchat.freenode.net/#octave.

* _config.yml: Remove obsolte entries.
* pages/menu/get-involved.md: Update URL.
* pages/menu/support.md: Update URL.

Author: siko1056

_config.yml

@@ -19,8 +19,6 @@ sourceforge_url: "https://octave.sourceforge.io"
 packages_url: "https://gnu-octave.github.io/packages/"
 maintainers_email: "[email protected]"
 help_email: "[email protected]"
-irc_channel: "#octave"
-irc_network: "irc.freenode.net"
 timezone: "UTC0"
 
 # Build settings

pages/menu/get-involved.md

@@ -24,7 +24,7 @@ and a [Developer FAQ]({{ site.wiki_url }}/Developer_FAQ).
 
 Discuss your ideas with us on [Discourse]({{ site.discourse_url }})
 ("maintainers" category) or on our IRC
-[Freenode `{{ site.irc_channel }}` channel](https://webchat.freenode.net/#octave).
+[Libera `#octave` channel](https://web.libera.chat/#octave).
 
 
 ### Get the Development Sources

pages/menu/support.md

@@ -34,7 +34,7 @@ available to you.
 - [<i class="fab fa-discourse"></i> **Discourse**]({{ site.discourse_url }}) --
   the major communication platform for Octave users and developers.
 - <i class="far fa-comments"></i> **IRC**: Chat with users and developers on the
-  [Freenode {{ site.irc_channel }} channel](https://webchat.freenode.net/#octave).
+  [Libera `#octave` channel](https://web.libera.chat/#octave).
 - <i class="far fa-envelope"></i> Browse the old
   [**mailing list archives**](https://lists.gnu.org/archive/html/help-octave/).
 </div>