tiered_abort was created as a clone of timestamp_abort, and "tiered storage" features were added to it, and some other features (like prepare) were dropped. We decided that to do real testing of tiered storage, we need all the features of timestamp_abort, including prepare, and it makes more sense to have a single program that incorporates a "tiered" mode.

Timestamp_abort has been improved via WT-9882, WT-10073, WT-9910 to have tiered features. For this ticket, we need to make sure we've covered the things that tiered_abort uniquely does (or did) and make sure that timestamp_abort is run in "tiered mode" within evergreen as appropriate. Also as part of this ticket, we should remove tiered_abort once we have the same coverage.