Cleanup unused SyncSeatLinkRequestWorker#update_code_suggestions_tokens

This method is no longer used: https://gitlab.com/gitlab-org/gitlab/-/blob/eae7739ac1c5d0eee0e78f53cbb19e87f34816ae/ee/app/workers/sync_seat_link_request_worker.rb#L103

Noticed by Corinna: Slack

We should drop it.

Related code change history diff: eae7739a