AP_Arming: don't show the GPS arming error in SITL

it just makes users think something is wrong

libraries/AP_Arming/AP_Arming.cpp

@@ -339,6 +339,7 @@ bool AP_Arming::gps_checks(bool report)
         }
     }
 
+#if CONFIG_HAL_BOARD != HAL_BOARD_SITL
     if ((checks_to_perform & ARMING_CHECK_ALL) || (checks_to_perform & ARMING_CHECK_GPS_CONFIG)) {
         uint8_t first_unconfigured = gps.first_unconfigured_gps();
         if (first_unconfigured != AP_GPS::GPS_ALL_CONFIGURED) {
@@ -348,11 +349,10 @@ bool AP_Arming::gps_checks(bool report)
                                                   first_unconfigured + 1);
                 gps.broadcast_first_configuration_failure_reason();
             }
-#if CONFIG_HAL_BOARD != HAL_BOARD_SITL
             return false;
-#endif
         }
     }
+#endif
     return true;
 }