Bug 29510: (follow-up) Adapt GET /patrons/:patron_id

Bug 29510: (follow-up) Adapt GET /patrons/:patron_id

This patch makes GET /patrons/:patron_id rely on this new behavior from the
objects.find helper.

To test:
1. Run:
   $ kshell
  k$ prove t/db_dependent/api/v1/patrons.t
=> SUCCESS: Tests pass!
2. Apply this patch
3. Repeat 1
=> SUCCESS: Tests still pass!
4. Sign off :-D

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
(cherry picked from commit 62df2689de670b81539a3569b0c8ec9e744d3170)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>