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/cppeditor/cppincludehierarchy.h

@@ -23,8 +23,7 @@
 **
 ****************************************************************************/
 
-#ifndef CPPINCLUDEHIERARCHY_H
-#define CPPINCLUDEHIERARCHY_H
+#pragma once
 
 #include <coreplugin/inavigationwidgetfactory.h>
 
@@ -111,5 +110,3 @@ public:
 
 } // namespace Internal
 } // namespace CppEditor
-
-#endif // CPPINCLUDEHIERARCHY_H