GPUSmoothing → Smoothing Relation

File in ITK/Modules/Filtering/GPUSmoothing	Includes file in ITK/Modules/Filtering/Smoothing
include / itkGPUDiscreteGaussianImageFilter.h	include / itkDiscreteGaussianImageFilter.h
include / itkGPUMeanImageFilter.h	include / itkMeanImageFilter.h