Bug 25048: Make successful resource deletion return 204

Bug 25048: Make successful resource deletion return 204

This patch adapts the spec and the controllers so existing routes return
204 and an empty response body when a successful deletion happens.

Right now we have a coding guideline but haven't adapted the existing
routes.

To test:
1. Apply the regression tests patch
2. Run:
   $ kshell
  k$ prove t/db_dependent/api/v1/*.t
=> FAIL: Some tests fail
3. Apply this patch
4. Repeat 2.
=> SUCCESS: Tests pass!
5. Sign off :-D

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>