DOC: Remove recursive inclusion of .h files

The .h files include the .hxx files, which in
turn include the original .h file.

Remove the recursive includes.

Following the change in ITK:
InsightSoftwareConsortium/ITK@eec8968

SoftwareGuide/Latex/Appendices/CodingStyleGuide.tex

@@ -1877,7 +1877,6 @@ \subsection{Class Layout}
 #ifndef itkImage_hxx
 #define itkImage_hxx
 
-#include "itkImage.h"
 #include "itkProcessObject.h"
 
 #include <algorithm>
@@ -2789,7 +2788,6 @@ \subsection{Empty Lines}
 #ifndef itkSpecializedImageFilter_hxx
 #define itkSpecializedImageFilter_hxx
 
-#include "itkSpecializedImageFilter.h"
 #include "itkProgressAccumulator.h"
 
 namespace itk