Remove :release_edit_page Feature Flag

What does this MR do?

Removes the :release_edit_page feature flag, as it is currently enabled by default, completing the feature's rollout.

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.
• Tested in all supported browsers

#36527 (closed)