Note that this is currently a proposal, discussion/push back is welcomed.

The WT_TXNID_LT and WT_TXNID_LE used to contain special handling for transaction IDs like WT_TXN_ABORTED and WT_TXN_NONE, however these days they just evaluate to `a < b` and `a <= b` respectively. This looks like a candidate to remove the macros and use `<`, `<=` comparisons directly.