Bug 17501: Use Koha::Object in Koha::Upload::_delete

Bug 17501: Use Koha::Object in Koha::Upload::_delete

Note: This is the last occurrence where we use DBI to perform a CRUD
operation. In this case a delete from uploaded_files.

We now call Koha::UploadedFile[s]->delete to only delete the record
from the table. A next step will be moving the additional functionality
of removing the file(s) too.

Test plan:
[1] Run t/db_dependent/Upload.t
[2] Delete an upload from tools/upload.pl

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>