don't store ROW END timestamp in PARTITION CURRENT

in a table that is partitioned BY SYSTEM_TIME, in a CURRENT partition the value of the column that is GENERATED ALWAYS AS ROW END is always the same, the max possible value for a given temporal type.

It doesn't make much sense to store this column in the table, it could be filled in after the row is read, much like a virtual generated column. And there is no point in appending it to all unique indexes — not doing it will make keys smaller and will competly eliminate the overhead for selects (currently sysbench oltp_read_only shows up to 20% slowdown).