[conf] ardrone2_raw: remove wrong NPS_JSBSIM_MODEL

We are still missing a JSBSim model for a quadrotor in X configuration (like the ARDrone2).
The "simple_quad" model is for + configuration.

Now you will get an error starting the NPS sim
(JSBSim failed to open the configuration file: foo/paparazzi/conf/simulator/jsbsim/aircraft/ardrone2_raw.xml).
But IMHO that is better than NPS just not working for no obvious reason.