Bug 14321: [QA Follow-up] Changes for Upload.pm and upload-file.pl

Bug 14321: [QA Follow-up] Changes for Upload.pm and upload-file.pl

Based on QA comments, this patch does the following:
[1] Destroy an empty DESTROY.
[2] Promote some comment lines to POD.
[3] Use File::Spec->catfile in sub _full_fname.
[4] Remove variable interpolation from a sql query.
[5] Add a comment in upload-file.pl.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Run the unit test again, and uploaded a file.

Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>