KWSys: Require at least CMake 2.6.3
KWSys: Require at least CMake 2.6.3

Remove code left for supporting earlier CMake versions.

biddisco/VTK,candy7393/VTK,jmerkow/VTK,demarle/VTK,gram526/VTK,keithroe/vtkoptix,cjh1/VTK,daviddoria/PointGraphsPhase1,daviddoria/PointGraphsPhase1,ashray/VTK-EVM,ashray/VTK-EVM,berendkleinhaneveld/VTK,mspark93/VTK,jmerkow/VTK,berendkleinhaneveld/VTK,gram526/VTK,biddisco/VTK,candy7393/VTK,cjh1/VTK,sumedhasingla/VTK,mspark93/VTK,sumedhasingla/VTK,SimVascular/VTK,johnkit/vtk-dev,ashray/VTK-EVM,mspark93/VTK,SimVascular/VTK,gram526/VTK,cjh1/VTK,cjh1/VTK,collects/VTK,hendradarwin/VTK,jmerkow/VTK,sankhesh/VTK,keithroe/vtkoptix,sankhesh/VTK,candy7393/VTK,spthaolt/VTK,SimVascular/VTK,johnkit/vtk-dev,aashish24/VTK-old,spthaolt/VTK,biddisco/VTK,berendkleinhaneveld/VTK,jmerkow/VTK,demarle/VTK,sankhesh/VTK,sumedhasingla/VTK,demarle/VTK,keithroe/vtkoptix,keithroe/vtkoptix,collects/VTK,berendkleinhaneveld/VTK,keithroe/vtkoptix,sumedhasingla/VTK,jmerkow/VTK,candy7393/VTK,msmolens/VTK,keithroe/vtkoptix,johnkit/vtk-dev,jmerkow/VTK,SimVascular/VTK,johnkit/vtk-dev,spthaolt/VTK,SimVascular/VTK,sumedhasingla/VTK,msmolens/VTK,johnkit/vtk-dev,hendradarwin/VTK,mspark93/VTK,msmolens/VTK,candy7393/VTK,keithroe/vtkoptix,daviddoria/PointGraphsPhase1,ashray/VTK-EVM,berendkleinhaneveld/VTK,biddisco/VTK,gram526/VTK,demarle/VTK,johnkit/vtk-dev,msmolens/VTK,hendradarwin/VTK,biddisco/VTK,collects/VTK,berendkleinhaneveld/VTK,hendradarwin/VTK,aashish24/VTK-old,msmolens/VTK,msmolens/VTK,mspark93/VTK,sumedhasingla/VTK,sankhesh/VTK,hendradarwin/VTK,jmerkow/VTK,gram526/VTK,collects/VTK,daviddoria/PointGraphsPhase1,biddisco/VTK,candy7393/VTK,mspark93/VTK,mspark93/VTK,hendradarwin/VTK,johnkit/vtk-dev,SimVascular/VTK,sankhesh/VTK,gram526/VTK,biddisco/VTK,ashray/VTK-EVM,msmolens/VTK,spthaolt/VTK,hendradarwin/VTK,sankhesh/VTK,daviddoria/PointGraphsPhase1,aashish24/VTK-old,collects/VTK,spthaolt/VTK,ashray/VTK-EVM,cjh1/VTK,SimVascular/VTK,demarle/VTK,sankhesh/VTK,gram526/VTK,ashray/VTK-EVM,gram526/VTK,demarle/VTK,aashish24/VTK-old,candy7393/VTK,sumedhasingla/VTK,demarle/VTK,SimVascular/VTK,spthaolt/VTK,candy7393/VTK,msmolens/VTK,spthaolt/VTK,aashish24/VTK-old,keithroe/vtkoptix,mspark93/VTK,aashish24/VTK-old,collects/VTK,berendkleinhaneveld/VTK,jmerkow/VTK,sankhesh/VTK,ashray/VTK-EVM,sumedhasingla/VTK,daviddoria/PointGraphsPhase1,cjh1/VTK,demarle/VTK