Bug 27330: (follow-up) Cleanup missed on bug 23843

Bug 27330: (follow-up) Cleanup missed on bug 23843

This patch makes some cleanup missed on bug 23843. The catch condition
on the controller was copied and pasted from other controller and should
be avoided unless there's a known case that needs special handling.
Otherwise it will be catched by the $c->unhandled_exception call.

All the old mappings were inadvertedly kept in the controller as well as
the (unused) _to_api method.

The base class is also cleaned from unnecessary mappings. Only mapped
things need to be added.

To test:
1. Apply this patch
2. Run:
   $ kshell
  k$ prove t/db_dependent/api/v1/clubs_holds.t \
           t/db_dependent/Koha/Club/Hold.t
=> SUCCESS: Tests pass!
3. Sign off :-D

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit f2593558952909f6c8df5d2ed8c6fea60cf7dcb9)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>