Don't enable VPN mode for the whole system as default

I'm not sure how/why, but when I enabled VPN mode, it tryed to routed my whole system through Tor. Also, my system was left hooked into Orbot even after I shut it down.

The combination of these two caused a lot of frustration until I found out I had to remove the system from the list of VPN mode-enabled apps.

I propose ensuring that VPN mode is not enabled for the whole system when someone turns it on for the first time (or, at least, not without a warning).