Arvados

• 'id' - most tables have a default 'id' column added by rails, despite the fact that 'uuid' is the real primary key
• 'updated_at' - this was removed from API responses in #15397

• humans, specimens, traits, jobs, job_tasks, pipeline_instances, pipeline_templates, keep_disks, nodes, repositories

#15397 (release 3.0) removed rails code that relied on the above tables/columns, so it will be safe to remove the tables themselves after 3.0 (see #15397#note-72).

api_clients table is not part of this -- see #21910.