Removes FF and condition

What does this MR do?

1. Removes [attributes[:scheduling_type] ||= build.find_legacy_scheduling_type]
2. Removes ci_ensure_scheduling_type FF

Does this MR meet the acceptance criteria?

Conformity

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

#217930 (closed)