ROMFS: clean up quad x tailsitter mixer files

- use mixer for the simulation to the sitl mixer dir
- do not use virtual elevator in the mixer for the real vehicle

Signed-off-by: Roman <bapstroman@gmail.com>

ROMFS/px4fmu_common/mixers/CMakeLists.txt

@@ -75,7 +75,6 @@ px4_add_romfs_files(
 	quad_x_can.main.mix
 	quad_x.main.mix
 	quad_x_vtol.main.mix
-	quad_x_vtol_sim.main.mix
 	stampede.main.mix
 	tri_y_yaw-.main.mix
 	tri_y_yaw+.main.mix