* MiG-15bis.xml (the JSBsim FDM): in Yaw channel, remove an
unnecessary stage between rudder command inputs and rudder surface
position (i.e. eliminate fcs/rudder-command-sum).
* Nasal/MiG-15bis.nas: s/weght/weight/ and remove unused properties
fdm/jsbsim/accelerations/Nz-max-tenth and
instrumentation/pedals/serviceable.