Rover: avoid using struct Location

clang reports this could be a problem when compiling under some EABIs.  Remove it from most places as it is just noise, replace with class where we want to avoid including Location.h

Rover/Rover.h

@@ -156,7 +156,7 @@ private:
     RC_Channels_Rover &rc() { return g2.rc_channels; }
 
     // The rover's current location
-    struct Location current_loc;
+    Location current_loc;
 
     // Camera
 #if AP_CAMERA_ENABLED