Remove references to the old mailing list

CONTRIBUTING.md

@@ -16,13 +16,6 @@ categories for discussions:
   feature request
 * **Q&A** - Request help with installing or using NetBox
 
-### Mailing List
-
-We also have a Google Groups [mailing list](https://groups.google.com/g/netbox-discuss)
-for general discussion, however we're encouraging people to use GitHub
-discussions where possible, as it's much easier for newcomers to review past
-discussions.
-
 ### Slack
 
 For real-time chat, you can join the **#netbox** Slack channel on [NetDev Community](https://netdev.chat/).

README.md

@@ -68,7 +68,6 @@ The complete documentation for NetBox can be found at [Read the Docs](https://ne
 
 * [GitHub Discussions](https://github.com/netbox-community/netbox/discussions) - Discussion forum hosted by GitHub; ideal for Q&A and other structured discussions
 * [Slack](https://netdev.chat/) - Real-time chat hosted by the NetDev Community; best for unstructured discussion or just hanging out
-* [Google Group](https://groups.google.com/g/netbox-discuss) - Legacy mailing list; slowly being replaced by GitHub discussions
 
 ### Installation
 

docs/development/index.md

@@ -7,9 +7,8 @@ NetBox is maintained as a [GitHub project](https://github.com/netbox-community/n
 There are several official forums for communication among the developers and community members:
 
 * [GitHub issues](https://github.com/netbox-community/netbox/issues) - All feature requests, bug reports, and other substantial changes to the code base **must** be documented in a GitHub issue.
-* [GitHub Discussions](https://github.com/netbox-community/netbox/discussions) - The preferred forum for general discussion and support issues. Ideal for shaping a feature request prior to submitting an issue.
+* [GitHub discussions](https://github.com/netbox-community/netbox/discussions) - The preferred forum for general discussion and support issues. Ideal for shaping a feature request prior to submitting an issue.
 * [#netbox on NetDev Community Slack](https://netdev.chat/) - Good for quick chats. Avoid any discussion that might need to be referenced later on, as the chat history is not retained long.
-* [Google Group](https://groups.google.com/g/netbox-discuss) - Legacy mailing list; slowly being phased out in favor of GitHub discussions.
 
 ## Governance