Nextcloud: Group admins can remove arbitrary data from "data" directory (including admin data)

Steps to reproduce: 1. Create a new user and make him an admin of an arbitrary group 2. Log in as this new user 3. Create a new user "filesexternal", "appdatarandom-data", .. 4. Delete this user Result: The data/filesexternal / data/appdata.. folder is removed. Solution: Prevent creation of users...