I don’t believe there is a way currently to do this from the UI. I think you would be able to delete the staff action itself through the rails console if you have access.
You can find the id for the staff action either by checking the staff logs json (/admin/logs/staff_action_logs.json) or using a data explorer query to give you a list to pick it from:
SELECT *
FROM user_histories
WHERE action = 17 --action code for 'delete post'
ORDER BY created_at DESC
And then using that id in the rails console:
UserHistory.where(id:[ID]).delete_all
Though, reading your ask more closely, I think you could overwrite the ‘details’ section instead of deleting the log with something like this:
UserHistory.where(id:[ID]).update(details:"permanently deleted")