Major - P3 The "non-tombstone trailing byte" assert in clayered_deleted_decode was removed in WT-18130 to unblock MongoDB CI. Re-enable it here.
The reason we're not folding this into WT-18057: we'll want to hold off on re-enabling the assert until we're sure we don't have any issues with values stored in production, but we want to fix the modify path sooner.
