[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.

conf/airframes/ardrone2_raw.xml

@@ -206,7 +206,6 @@
   <section name="SIMULATOR" prefix="NPS_">
     <define name="ACTUATOR_NAMES" value="{&quot;top_left_motor&quot;, &quot;top_right_motor&quot;, &quot;bottom_right_motor&quot;, &quot;bottom_left_motor&quot;}"/>
     <define name="JSBSIM_INIT" value="&quot;reset00&quot;"/>
-    <define name="JSBSIM_MODEL" value="&quot;simple_quad&quot;"/>
     <define name="SENSORS_PARAMS" value="&quot;nps_sensors_params_default.h&quot;"/>
   </section>