COMP: Fix unused-local-typedefs warnings

vtkSlicerMultiVolumeExplorerLogic.cxx:188:28: warning: typedef ‘ImageIOType’ locally defined but not used [-Wunused-local-typedefs]
   typedef itk::GDCMImageIO ImageIOType;
                            ^
vtkSlicerMultiVolumeExplorerLogic.cxx:189:36: warning: typedef ‘InputNamesGeneratorType’ locally defined but not used [-Wunused-local-typedefs]
   typedef itk::GDCMSeriesFileNames InputNamesGeneratorType;
                                    ^
vtkSlicerMultiVolumeExplorerLogic.cxx:192:48: warning: typedef ‘ReaderType’ locally defined but not used [-Wunused-local-typedefs]
   typedef itk::ImageSeriesReader< VolumeType > ReaderType;