Fix wrong API status codes

What does this MR do?

This fixes the wrong documentation for different DELETE endpoints in the API.

Why was this MR needed?

Delete endpoints now return 204 instead of 200. This was not updated for all API calls in the documentation.

Does this MR meet the acceptance criteria?

• [-] Changelog entry added, if necessary
• Documentation created/updated
• [-] API support added
• [-] Tests added for this feature/bug
• Review
  • [-] Has been reviewed by UX
  • [-] Has been reviewed by Frontend
  • Has been reviewed by Backend
  • [-] Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together