Once enough time has passed since T361206: Stop writing old for user agent schema migration on WMF wikis, the agent column (e.g. cuc_agent, cupe_agent) should be removed from the CheckUser result tables (e.g. cu_changes, cu_log_event).
Acceptance criteria
- The cuc_agent, cule_agent, and cupe_agent columns are removed from the cu_changes, cu_log_event and cu_private_event tables respectively.