Drop useless plasma fuel code

src/vehicle.cpp

@@ -49,7 +49,6 @@ static const itype_id fuel_type_gasoline("gasoline");
static const itype_id fuel_type_diesel("diesel");
static const itype_id fuel_type_battery("battery");
static const itype_id fuel_type_plutonium("plut_cell");
static const itype_id fuel_type_plasma("plasma");
static const itype_id fuel_type_water("water_clean");
static const itype_id fuel_type_muscle("muscle");
static const std::string part_location_structure("structure");
@@ -2842,7 +2841,7 @@ int vehicle::drain (const itype_id & ftype, int amount) {
        }
    }

    if( ftype != fuel_type_battery && ftype != fuel_type_plasma ) {
    if( ftype != fuel_type_battery ) {
        invalidate_mass();
    }

@@ -3043,8 +3042,6 @@ void vehicle::noise_and_smoke( double load )
                    mufflesmoke += j;
                }
                pwr = (cur_pwr*15 + max_pwr*3 + 5) * muffle;
            } else if(is_engine_type(e, fuel_type_plasma)) {
                pwr = (cur_pwr*9 + 1) * muffle;
            } else if(is_engine_type(e, fuel_type_battery)) {
                pwr = cur_pwr*3;
            } else if(is_engine_type(e, fuel_type_muscle)) {
@@ -5350,8 +5347,7 @@ bool vehicle::explode_fuel( int p, damage_type type )

    static const std::map<itype_id, fuel_explosion> explosive_fuels = {{
        { fuel_type_gasoline,   { 2, 5, 1.0f, true, 0.1f } },
        { fuel_type_diesel,     { 20, 1000, 0.2f, false, 0.1f } },
        { fuel_type_plasma,     { 1, 2, 1.4f, false, 1.0f } }
        { fuel_type_diesel,     { 20, 1000, 0.2f, false, 0.1f } }
    }};

    const auto iter = explosive_fuels.find( ft );