rm fwd decl

Device/Mask/MaskStack.h

@@ -18,11 +18,9 @@
 #ifndef BORNAGAIN_DEVICE_MASK_MASKSTACK_H
 #define BORNAGAIN_DEVICE_MASK_MASKSTACK_H
 
-#include <memory>
-
 #include "Base/Types/CloneableVector.h"
+#include <memory>
 
-class Datafield;
 class IShape2D;
 class Scale;