AP_NavEKF3: clarify yaw reset error message

The current wording can be taken to indicate that the mag sensors
stopped, causing this issue.

libraries/AP_NavEKF3/AP_NavEKF3_MagFusion.cpp

@@ -1493,7 +1493,7 @@ bool NavEKF3_core::EKFGSF_resetMainFilterYaw()
         if (effectiveMagCal == MagCal::GSF_YAW || AP::compass().get_num_enabled() == 0) {
             gcs().send_text(MAV_SEVERITY_INFO, "EKF3 IMU%u yaw aligned using GPS",(unsigned)imu_index);
         } else {
-            gcs().send_text(MAV_SEVERITY_WARNING, "EKF3 IMU%u emergency yaw reset - mag sensor stopped",(unsigned)imu_index);
+            gcs().send_text(MAV_SEVERITY_WARNING, "EKF3 IMU%u emergency yaw reset",(unsigned)imu_index);
         }
 
         // Fail the magnetomer so it doesn't get used and pull the yaw away from the correct value