As far as I am aware, there is no way to turn off reflection on the environment light itself. The solution to your problem would be to set reflection masks on the geometry node that holds the car geometry.
You will find that option on the geometry node under the tab Render > Shading. By default it has a * in it, but if you just select the objects you want the geometry to reflect it should work.
Hope this helps.
EDIT: On second though I actually believe you can go to the light tab on your environment light, and then click the option "light contribution". The name light contribution is a little misleading as far as I remember. If you choose reflection as light contribution I seem to remember that the light will NOT reflect. Anybody correct me if I am wrong.
Again hope this helps