Cleans up one_dimensional_matrix feature flag

What does this MR do?

Cleans up the one_dimensional_matrix feature flag code Rollout issue: #256062 (closed)

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

#267641 (closed)