STYLE: Remove unnecessary using type aliases from enum definitions

In C, it might be useful to add such type aliases to `enum`
definitions, but it is unnecessary in C++.

This commit also removed unnecessary empty lines of code from those enum
definitions.

Modules/Filtering/FFT/include/itkComplexToComplex1DFFTImageFilter.h

@@ -68,7 +68,11 @@ class ITK_TEMPLATE_EXPORT ComplexToComplex1DFFTImageFilter : public ImageToImage
   itkFactoryOnlyNewMacro(Self);
 
   /** Transform direction. */
-  using TransformDirectionType = enum { DIRECT = 1, INVERSE };
+  enum TransformDirectionType
+  {
+    DIRECT = 1,
+    INVERSE
+  };
 
   /** Set/Get the direction in which the transform will be applied.
    * By selecting DIRECT, this filter will perform a direct (forward) Fourier

Modules/IO/ImageBase/include/itkIOCommon.h

@@ -67,14 +67,10 @@ extern ITKIOImageBase_EXPORT std::ostream &
 class ITKIOImageBase_EXPORT IOCommon
 {
 public:
-  using SysConstants = enum
-
+  enum SysConstants
   {
-
     ITK_MAXPATHLEN = 2048, /**< Maximum length of a filename */
-
     MAX_FILENAMELIST_SIZE = 512
-
   };
 
   using AtomicPixelEnum = IOCommonEnums::AtomicPixel;