Medical Feedback - Fix DISABLE_VANILLA_DAMAGE_EFFECTS

[PabstMirror]

DISABLE_VANILLA_DAMAGE_EFFECTS was only defined in medical_feedback
so it wasn't running, and I'm pretty sure this is where it belongs
it's also now under a hasInterface check

[commy2]

Don't know what the UAV pilot thing does here, but looks good to me.

[PabstMirror]

ai would be handled inside the init:

        if (getText (_config >> "simulation") == "UAVPilot") exitWith {TRACE_1("ignore UAV AI",typeOf _unit);};

this just skips adding the initEH to AI classes

also pushed a small change to keep the old var name
_unit setVariable [QEGVAR(medical,lastDamageSource), _shooter];
to ensure compatiblity with acex_killtracker and possibly other missions that would use this var to determine killer