Bug 28962: Add del-unv-selfreg to crontab

Bug 28962: Add del-unv-selfreg to crontab

We also add a test by inserting a simulated borrower modification
record in the same table which should not be deleted.

NOTE: This patch fixes the del-unv-selfreg parameter in the
cleanup db script. It did not even do what it promised :)

Test plan:
Verify if the crontab change is correct.
Run t/db_dependent/Members.t

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>