Clean up unnecessary entries in the UndoBuffer chain

[Mytherin]

Right now if a single transaction updates the same tuple twice (i.e. runs the following two queries)
BEGIN TRANSACTION;
UPDATE integers SET i=4 WHERE i=3;
UPDATE integers SET i=5 WHERE i=4;
The tuple will have two entries in the version chain; but the first entry is useless as it will never be required by a different transaction.

[github-actions]

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[github-actions]

This issue was closed because it has been stale for 30 days with no activity.