Remove help message about prioritized labels for non-members

What does this MR do?

Remove help message about prioritized labels for non-members.

Are there points in the code the reviewer needs to double check?

No.

Why was this MR needed?

To improve non-members' UX in project labels.

Screenshots (if relevant)

conditions	screenshots
before
after (for member)
after (for non-member)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [n/a] Documentation created/updated
• [n/a] API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #35191 (closed)