Use global feature flag for fast destroy

What does this MR do?

Rolling out fast destroy feature is not ideal if this feature is scoped to a specific project/group because uploads are typically scoped to project or group, so we would have to enable this feature for a project which is going to be destroyed (which we don't know in front).

This feature flag was introduced in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/20977

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer