Bug 17992: REST api: Remove the use of ->unblessed from Cities controller

Bug 17992: REST api: Remove the use of ->unblessed from Cities controller

As bug 17932 adds TO_JSON to Koha::Object(s), there's no need for using
it. Also, as this is a reference implementation for developers to copy
and paste it is sensible to make this change even when this is not
causing any bug.

To test:
- Apply the patch
- Run:
  $ sudo koha-shell kohadev
 k$ cd kohaclone
 k$ prove t/db_dependent/api/v1/cities.t
=> SUCCESS: Tests still pass!
- Sign off :-D

Signed-off-by: Matthias Meusburger <matthias.meusburger@biblibre.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>