Bug 17669: Small change to sub delete

Bug 17669: Small change to sub delete

Instead of looping through _resultset here and wrapping the results,
we should use a Koha::Objects instance. Since the method may be called
as a class method, we create an instance if needed.

Test plan:
Run t/db_dependent/Upload.t

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Mirko Tietgen <mirko@abunchofthings.net>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>