AP_Frsky_Telem: replace header guard with pragma once

libraries/AP_Frsky_Telem/AP_Frsky_Telem.h

@@ -13,9 +13,7 @@
    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
-
-#ifndef __AP_FRSKY_TELEM_H__
-#define __AP_FRSKY_TELEM_H__
+#pragma once
 
 #include <AP_HAL/AP_HAL.h>
 #include <AP_Param/AP_Param.h>
@@ -184,4 +182,3 @@ private:
 
     uint8_t _sport_status;
 };
-#endif