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/imageviewer/imageviewerconstants.h

@@ -24,8 +24,7 @@
 **
 ****************************************************************************/
 
-#ifndef IMAGEVIEWERCONSTANTS_H
-#define IMAGEVIEWERCONSTANTS_H
+#pragma once
 
 namespace ImageViewer {
 namespace Constants {
@@ -44,5 +43,3 @@ const char ACTION_TOGGLE_ANIMATION[] = "ImageViewer.ToggleAnimation";
 
 } // namespace Constants
 } // namespace ImageViewer
-
-#endif // IMAGEVIEWERCONSTANTS_H