Fix self-attached GPS trackers in vehicle

[dedmen]

Added feature in #29 to attach GPS tracker to self.
But when player enters a vehicle it gets deleted, and recreated when player exits the vehicle.
It should instead just temporarily be attached to the vehicle instead.

Ref
https://github.com/acemod/ACE3/blob/master/addons/attach/functions/fnc_handleGetIn.sqf#L31
acemod/ACE3#8476