COMP: No longer disable obsolete MSVC warning C4231 on 'extern' template
COMP: No longer disable obsolete MSVC warning C4231 on 'extern' template

MSVC 2015, 2017, and 2019 no longer produce this particular warning.

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