Clean up test run code in AI Catalog

What does this MR do and why?

Remove unused mutation, mock data, copy, and constant. Previous MR: !210702 (merged)

References

Slack: https://gitlab.slack.com/archives/C08T5J1KXKQ/p1761854835062219

Screenshots or screen recordings

Minor change in copy.

How to set up and validate locally

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