This script has a pattern to delete rows depending on a given
date/number of days, we should use the filter_by_last_update
Koha::Objects method.
No need for another method and tests, everything is already tested
there.
This patch also suggests to rename the reference to "background" and
"bg" with "jobs", which seems more appropriate and not an abbreviation
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
