Standardize audio notices to use 'System NUMBER'.

Otherwise some messages say 'System MAV 0-20' and some say 'System 20'.

src/uas/UAS.cc

@@ -1209,7 +1209,7 @@ void UAS::receiveMessage(LinkInterface* link, mavlink_message_t message)
             mavlink_mission_item_reached_t wpr;
             mavlink_msg_mission_item_reached_decode(&message, &wpr);
             waypointManager.handleWaypointReached(message.sysid, message.compid, &wpr);
-            QString text = QString("System %1 reached waypoint %2").arg(getUASName()).arg(wpr.seq);
+            QString text = QString("System %1 reached waypoint %2").arg(getUASID()).arg(wpr.seq);
             GAudioOutput::instance()->say(text);
             emit textMessageReceived(message.sysid, message.compid, MAV_SEVERITY_INFO, text);
         }
@@ -3360,7 +3360,7 @@ void UAS::startLowBattAlarm()
 {
     if (!lowBattAlarm)
     {
-        GAudioOutput::instance()->alert(tr("system %1 has low battery").arg(getUASName()));
+        GAudioOutput::instance()->alert(tr("System %1 has low battery").arg(getUASID()));
         QTimer::singleShot(3000, GAudioOutput::instance(), SLOT(startEmergency()));
         lowBattAlarm = true;
     }