CourseOverview will only delete old versions of saved data.

Previously, CourseOverview would delete data for any version
that didn't match the current one. That could cause problems
during deploys, when multiple versions of CourseOverview
were active. They would overwrite each other, and that could
cause problems if the old one overwrote the new one -- in
our case, the new one created a new table with foreign key
links that the old one was unaware of, and trying to delete
it would have caused an error.