Remove CI API v1

What does this MR do?

Remove the deprecated API

Why was this MR needed?

We have to remove it some day, with the %10.0 coming, now is as good as ever.

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

What are the relevant issue numbers?