Bug 25513: Remove unneeded integer casting in Koha::Object->TO_JSON

Bug 25513: Remove unneeded integer casting in Koha::Object->TO_JSON

This patch removes a problematic integer casting happening in TO_JSON.
The original need for this cast (a DBD::mysql bug) is now fixed. We
remove the cast as it is causing random failures.

To test:
1. Apply the regression tests
2. Run:
   $ kshell
  k$ prove t/db_dependent/api/v1/acquisitions_orders.t
=> FAIL: Tests fail with select high values (i.e. casting gives wrong
        results)
3. Apply this patch
4. Repeat 2
=> SUCCESS: Tests now pass!
5. Sign off :-D

Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>