Bug 24321: Make objects.search use mappings from Koha::Object(s)

Bug 24321: Make objects.search use mappings from Koha::Object(s)

This patch simplifies the objects.search helper so it relies entirely on
the result set object for the attribute mappings.

The result is no more to_api or to_model mappings are passed. The
controllers need to be cleaned up after this patch.

To test:
1. Apply this patch
2. Run:
   $ kshell
  k$ prove t/db_dependent/Koha/REST/Plugin/Objects.t
=> SUCCESS: Tests pass!
3. Sign off :-D

Note: the original version of this helpers accepted arbitrary mappings
and are now constrianed to real mappings on the Koha::Object level. As
such, the number of tests got reduced.

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>