As @tgrabiec helpfully pointed out, creating a row tombstone
for a table which does not have a clustering key in its schema
creates something that looks like an open-ended range tombstone.
That's problematic for KA/LA sstable formats, which are incapable
of writing such tombstones, so a workaround is provided
in order to allow using KA/LA in alternator.
Fixes#6035
(cherry picked from commit 0a2d7addc0)
1bd79705fb