STYLE: Remove unnecessary implementation file manual instantiation guard
STYLE: Remove unnecessary implementation file manual instantiation guard

Remove duplicate, commented implementation file manual instantiation
guard.

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