STYLE: Replace type aliases with `using`-declarations, in itkIntTypes.h
STYLE: Replace type aliases with `using`-declarations, in itkIntTypes.h

Reduced code redundancy by replacing type alias declarations of the form
`using` _type_ `= std::`_type_ with the equivalent `using`-declarations.

richardbeare/ITK,hjmjohnson/ITK,hjmjohnson/ITK,Kitware/ITK,richardbeare/ITK,InsightSoftwareConsortium/ITK,richardbeare/ITK,BRAINSia/ITK,hjmjohnson/ITK,BRAINSia/ITK,thewtex/ITK,hjmjohnson/ITK,BRAINSia/ITK,richardbeare/ITK,thewtex/ITK,thewtex/ITK,BRAINSia/ITK,thewtex/ITK,hjmjohnson/ITK,Kitware/ITK,Kitware/ITK,BRAINSia/ITK,Kitware/ITK,thewtex/ITK,hjmjohnson/ITK,thewtex/ITK,hjmjohnson/ITK,BRAINSia/ITK,richardbeare/ITK,InsightSoftwareConsortium/ITK,Kitware/ITK,InsightSoftwareConsortium/ITK,InsightSoftwareConsortium/ITK,InsightSoftwareConsortium/ITK,thewtex/ITK,InsightSoftwareConsortium/ITK,richardbeare/ITK,Kitware/ITK,Kitware/ITK,richardbeare/ITK,InsightSoftwareConsortium/ITK,BRAINSia/ITK