Now that a timestamp of zero is reserved (WT-8973), we should be able to eliminate the has_durable_timestamp, has_oldest_timestamp and has_stable_timestamp booleans from the WT_TXN_GLOBAL structure, and use a timestamp of 0 as the not-set value instead. (We might be able to delete has_pinned_timestamp as well, but I doubt it.)

These are all shared memory updates, living on the same cache line, and likely impact timestamp set/get performance.