Bug 23916: (follow-up) Don't anonymise issuer and don't update action_logs on upgrade

Bug 23916: (follow-up) Don't anonymise issuer and don't update action_logs on upgrade

This commit implements the two suggestions made by Nick in comment #41:

- Removes the attempted retrospective addition of issuers to old issues.
It was not particularly reliable, it also is not appropriate if the user
does not wish to make use of this functionality

- Removes the conversion of a NULL issuer to the anonymous borrowernumber when
anonymising checkouts

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>