Remove obsolete config setting

[charisk]

We're no longer using this setting but the contributions part was accidentally left in.

Checklist

N/A:

• CHANGELOG.md has been updated to incorporate all user visible changes made by this pull request.
• Issues have been created for any UI or other user-facing changes made by this pull request.
• [Maintainers only] If this pull request makes user-facing changes that require documentation changes, open a corresponding docs pull request in the github/codeql repo and add the ready-for-doc-review label there.

[robertbrignull]

Worth noting that having unknown elements in your user settings is not an error, so removing this won't cause problems for anyone who has added this setting.