materialized views: simplify do_delete_old_entry()
materialized views: simplify do_delete_old_entry()

In previous patches, we gave up on an old (and broken) attempt to track
the timestamps of many unselected base-table columns through one row marker
in the view table - and replaced them by "virtual cells", one per unselected
cell.

The do_delete_old_entry() function still contains old code which maintained
that row marker, and is no longer needed. That old code is no only no longer
needed, it also no longer did anything because all columns now appear in
the view (as virtual columns) so the code ignored them when calculating the
row marker.

Signed-off-by: Nadav Har'El <625169824b719df98706d88646d0aae6f368ae4d@scylladb.com>
Message-Id: <20180829131914.16042-1-625169824b719df98706d88646d0aae6f368ae4d@scylladb.com>

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