docs(vehicle): revert the axis fix; the reverse is in the Chaos solver

The axis_forward:X / Blender-Z axle fix changed the reference pose but not the drive
(-2737 cm/s), and axis_forward:X also alters the shared character preset. Revert it.
The Chaos solver drives the wheel about the vehicle's Y (not the bone), and the
drive force is positive yet the car moves backward - the inversion is in the engine
torque / drive-force sign. Next: GetEngineTorque() sign or a SetupVehicle override.

Tools/unreal/ue_vehicle_import.py

@@ -119,11 +119,6 @@ def main():
         ui.import_animations = False
         ui.import_materials = True
         ui.skeletal_mesh_import_data.import_uniform_scale = 1.0
-        # The FBX is already authored in the Unreal frame (nose +X, axle along Y); the
-        # importer's default axis conversion otherwise rolls the armature 90 deg about X and
-        # the wheel axles land on Z, which drives the Chaos vehicle backward.
-        ui.skeletal_mesh_import_data.import_rotation = unreal.Rotator(0.0, 0.0, 0.0)
-        ui.skeletal_mesh_import_data.import_translation = unreal.Vector(0.0, 0.0, 0.0)
         task.options = ui
         unreal.AssetToolsHelpers.get_asset_tools().import_asset_tasks([task])
         skel = unreal.EditorAssetLibrary.load_asset(f"{DEST}/SK_Vehicle_Sedan")