[gps] for now, compute utm without nav_utm_zone0

This variable is only available on fixedwing. It is not really nice to
report GPS pos without using the ref zone, but the possible error is
only on display and logged values, internaly it is correct if relevant.

sw/airborne/subsystems/gps.c

@@ -25,7 +25,6 @@
  */
 
 #include "subsystems/gps.h"
-#include "subsystems/navigation/common_nav.h"
 #include "led.h"
 
 #ifdef GPS_POWER_GPIO
@@ -90,7 +89,7 @@ static void send_gps(struct transport_tx *trans, struct link_device *dev)
   uint8_t zero = 0;
   int16_t climb = -gps.ned_vel.z;
   int16_t course = (DegOfRad(gps.course) / ((int32_t)1e6));
-  struct UtmCoor_i utm = utm_int_from_gps(&gps, nav_utm_zone0);
+  struct UtmCoor_i utm = utm_int_from_gps(&gps, 0);
   pprz_msg_send_GPS(trans, dev, AC_ID, &gps.fix,
                     &utm.east, &utm.north,
                     &course, &gps.hmsl, &gps.gspeed, &climb,