Remove user_id param from the discover endpoint in the internal api

What does this MR do?

This removes the possibility to pass a user_id to the /internal/discover api call.

While I was doing that, I found some low hanging fruit for a query to optimize. I found it small enough to do in this single MR.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Closes #33647 (closed)