Bug 29859: Use iterator instead of as_list

Bug 29859: Use iterator instead of as_list

On bug 29844 we decided to remove wantarray from Koha::Objects->search.
Reviewing the difference occurrences I found some unnecessary uses of ->as_list,
where iterators should be used instead.

This patch only removes the obvious places, not the tricky ones.

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>