Remove show_inherited_labels FF

What does this MR do?

• it removes show_inherited_labels feature flag

The show_inherited_labels feature flag was defaulted to on in !45161 (merged) along with a changelog entry.

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

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.

Related to #267547 (closed)