Once T366546: Remove wgCheckUserEventTablesMigrationStage and related migration code and T366781: Run maintenance script to delete entries only for use when reading old on WMF wikis are complete, the cu_changes table will no longer have any rows that are only for use when reading old. This means that all the code does not need to exclude these rows, so conditions on cuc_only_for_read_old can be removed. There may be other code that also needs removing as part of this task.
Acceptance criteria
- Any remaining code to support event tables migration is removed