AP_Rally: replace header guard with pragma once

libraries/AP_Rally/AP_Rally.h

@@ -14,8 +14,7 @@
  * - provides access to the rally points, including logic to find the nearest one
  *
  */
-#ifndef AP_Rally_h
-#define AP_Rally_h
+#pragma once
 
 #include <AP_Common/AP_Common.h>
 #include <AP_Param/AP_Param.h>
@@ -75,6 +74,3 @@ private:
 
     uint32_t _last_change_time_ms;
 };
-
-
-#endif // AP_Rally_h