Use #pragma once

LibreOffice core uses that, too, and we support an even more
restricted set of compilers.

Change-Id: I0d0e2c8608e323eb5ef0f35ee8c46d02ab49a745
Reviewed-on: https://gerrit.libreoffice.org/c/online/+/92467
Tested-by: Jenkins CollaboraOffice <jenkinscollaboraoffice@gmail.com>
Reviewed-by: Tor Lillqvist <tml@collabora.com>

common/FileUtil.hpp

@@ -7,8 +7,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-#ifndef INCLUDED_FILEUTIL_HPP
-#define INCLUDED_FILEUTIL_HPP
+#pragma once
 
 #include <string>
 
@@ -98,6 +97,4 @@ namespace FileUtil
 
 } // end namespace FileUtil
 
-#endif
-
 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */