C++ modernize: Pragma once (#6264)

* Migrate cpp headers to pragma once

src/map_settings_manager.h

@@ -17,8 +17,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */
 
-#ifndef MAP_SETTINGS_MANAGER_HEADER
-#define MAP_SETTINGS_MANAGER_HEADER
+#pragma once
 
 #include <string>
 
@@ -75,5 +74,3 @@ private:
 	Settings *m_map_settings;
 	Settings *m_user_settings;
 };
-
-#endif