Bug 14215: Change the 'delimiter' syspref description for its wider use

Bug 14215: Change the 'delimiter' syspref description for its wider use

Patch changes 'report files' to 'CSV files' as there are more
options now for downloading and creating CSV files where this
preference is taken into account.

To test:
- Verify the changed system preference description for
  'delimiter' is correct.

Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Jonathan Druart <jonathan.druart@koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>