Remove IRC link from docs (#369)

Author: Andersson007

docs/contributor-guide.md

@@ -70,9 +70,7 @@ See the `tests/integration/test_container.py` for examples.
   - [News & Announcements](https://forum.ansible.com/c/news/5): track project-wide announcements including social events.
   - [Bullhorn newsletter](https://docs.ansible.com/ansible/devel/community/communication.html#the-bullhorn): used to announce releases and important changes.
 
-- We are also available on the following chat platforms:
-  - Matrix: in the [#devtools:ansible.com](https://matrix.to/#/#devtools:ansible.com) room.
-  - Libera.Chat: in the `#ansible-devtools` Libera.Chat IRC channel.
+- We are also available on Matrix in the [#devtools:ansible.com](https://matrix.to/#/#devtools:ansible.com) room.
 
 Possible security bugs should be reported via email to
 <mailto:[email protected]>.