Set danger variant to remove group confirmation

What does this MR do and why?

Update remove confirmation for groups to danger variant and change the label on remove button

Related to #344183 (closed)

Screenshots or screen recordings

Without FF	With FF

How to set up and validate locally

1. Enable the bootstrap_confirmation_modals feature flag: Feature.enable(:bootstrap_confirmation_modals)
2. Login as admin
3. Go to http://localhost:3000/admin/groups
4. Click 'Delete' next to one of the groups on the list
5. Check the confirmation modal

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.