- Setting 0660 as permissions of /dev/vboxusb directory itself was preventing
access to this directory by any non-root user, even if member of vboxusers.
This results in VBox UI failing to enable USB passthrough.
Fix issue by removing all the workarounds for /dev/vboxusb/* as they should
no longer be required.

I have verified that with this USB passhtrough works on today's TW (real machine), as well as Leap 15.5 (on a VM) and today's Leap 15.6 beta (unfortunately, I couldn't get a nested VM to work on 15.6 at all -- but with this fix the UI can enumerate USB devices at least).

Without this fix, VBox always shows "VirtualBox is not currently allowed to access USB devices. You can change this by adding your user to vboxusers [....]", and the UI cannot enumerate USB devices at all. (forwarded request 1163957 from javispedro)