Bug 19025: Move GetReserveInfo to Koha::Holds

Bug 19025: Move GetReserveInfo to Koha::Holds

This subroutine is only used once and can be replaced with a call to
Koha::Holds->find
It will avoid unnecessary joins.

Test plan:
- Define a HOLD_SLIP template notice using fields from the tables
reserves, branches, borrowers, biblio, biblioitems and items.
- Generate one and make sure the values are correctly filled

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>