Uninstall script doesn't remove group

Running the uninstall script with `sudo python3 uninstall.py`. Everything was reported as successful, however the group `anudeepND/whitelist` was not removed from PiHole, nor is it possible to remove it manually. Although the Web UI reports success after an attempt to remove it, if we refresh the browser, the group is still there.

While I haven't investigated, I have the feeling that this is somewhat related to #187

My fix was to remove it directly from `gravity.db` with `DELETE FROM "group" WHERE id = 2552552551;`