C++ modernize: Pragma once (#6264)

* Migrate cpp headers to pragma once

src/quicktune_shortcutter.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 QVT_SHORTCUTTER_HEADER
-#define QVT_SHORTCUTTER_HEADER
+#pragma once
 
 #include "quicktune.h"
 
@@ -83,6 +82,3 @@ public:
 		setQuicktuneValue(getSelectedName(), val);
 	}
 };
-
-#endif
-