Remove runner_instructions ff

What does this MR do?

This removes the runner_instructions feature flag for the runner instructions modal

This was introduced in: !51014 (merged)

#296818 (closed)

Screenshots (strongly suggested)

N/A

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content