Make delayed deletion available to all pricing tiers

What does this MR do and why?

This MR removes the downtier_delayed_deletion feature flag and makes delayed deletion available to all pricing tiers.

The feature flag was rolled out globally at 2025-04-29T15:28:55Z

There are a lot of changes here, but most are due to the deletion of EE tests. Previously, we maintained EE tests to ensure that the feature behaved as expected when the licensed feature was available. There are still references to the adjourned_deletion_for_projects_and_groups, but to keep this MR from getting any bigger, that will be cleaned up in a follow-up.

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Before	After

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Related to #526375 (closed)