Bug 37686: Fix render_resource_not_found() and render_resource_deleted() misses

Bug 37686: Fix render_resource_not_found() and render_resource_deleted() misses

This patch refactors some small pieces of code to use the helpers as
prescribed on our coding guidelines [1] instead of manually crafting
responses.

To test:
1. Apply this patch
2. Run:
   $ ktd --shell
  k$ prove t/db_dependent/api/v1/
=> SUCCESS: All tests pass
3. Sign off :-D

[1] https://wiki.koha-community.org/wiki/Coding_Guidelines_-_API#REST4:_Controller_code_.5BDRAFT.5D

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Matt Blenkinsop <matt.blenkinsop@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>