Resolve "rspec:feature-flag failure for migrate_delayed_project_removal" [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

Removes the migrate_delayed_project_removal feature flag yml since the usage of the feature flag was removed in !56397 (diffs)

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

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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
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Security

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• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
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Related to #326057 (closed)