connect_obd() set _car_ever_connected without a global declaration, so the
module-level flag was never set and was_car_ever_connected() always returned
False — local trip building has been silently blocked since BUG-10 landed.
Also persist the flag to the settings table so a drive followed by a reboot
still builds trips, and clean up dead code in was_car_ever_connected().
Mathieu Moran