Remove FF `always_perform_delayed_deletion`

What does this MR do and why?

Related to #393622 (closed)

Now that the always_perform_delayed_deletion has been enabled by default for a few days, we can remove this feature flag.

Follow up issue: #411206 (closed), to drop the columns related to delayed deletion, since they are no longer used.

Screenshots or screen recordings

Admin area

feature flag disabled	feature flag enabled	feature flag removed (this MR)

How to set up and validate locally

1. Go to /admin/application_settings/general and expand the Visibility and access controls section. There should be only an input for retention period.
2. Go to a group -> Settings -> General -> Permissions and group features. The Deletion protection setting shouldn't be rendered.

MR acceptance checklist

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