Remove myself as Discourse mod

[notriddle]

I haven't been putting the time in that I should, and mdBook is launching a new team that I'm probably going to be involved with.

[notriddle]

CC @steffahn @oli-obk

[oli-obk]

Thanks for the time you have spent on it all these years!

[github-actions]

Dry-run check results

[WARN  rust_team::sync] sync-team is running in dry mode, no changes will be applied.
[INFO  rust_team::sync] synchronizing crates-io
[INFO  rust_team::sync] synchronizing github
[INFO  rust_team::sync] 💻 Repo Diffs:
    📝 Editing repo 'rust-lang/rust':
      Environments:
        ❌ Delete: copilot

[steffahn]

Huge thank you from me as well!