Sub: Remove stale commented code

ArduSub/control_poshold.cpp

@@ -36,10 +36,6 @@ bool Sub::poshold_init(bool ignore_checks)
 void Sub::poshold_run()
 {
     uint32_t tnow = AP_HAL::millis();
-    // convert inertial nav earth-frame velocities to body-frame
-    //    const Vector3f& vel = inertial_nav.get_velocity();
-    //    float vel_fw = vel.x*ahrs.cos_yaw() + vel.y*ahrs.sin_yaw();
-    //    float vel_right = -vel.x*ahrs.sin_yaw() + vel.y*ahrs.cos_yaw();
 
     // if not auto armed set throttle to zero and exit immediately
     if (!motors.armed() || !ap.auto_armed) {