Wholesale conversion to #pragma once

Kudos to cgmb and https://github.com/cgmb/guardonce

Change-Id: Ifa8970734b8d43fd08c9260c645bdb0228633791
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>

src/plugins/cpptools/cppcodestylepreferencesfactory.h

@@ -23,8 +23,7 @@
 **
 ****************************************************************************/
 
-#ifndef CPPCODESTYLEPREFERENCESFACTORY_H
-#define CPPCODESTYLEPREFERENCESFACTORY_H
+#pragma once
 
 #include <texteditor/icodestylepreferencesfactory.h>
 
@@ -46,5 +45,3 @@ public:
 };
 
 } // namespace CppTools
-
-#endif // CPPCODESTYLEPREFERENCESFACTORY_H