COMP: remove custom set/get macros from vtkModelMetadata.h
COMP: remove custom set/get macros from vtkModelMetadata.h

This header file had two macros: myVtkGetMacro, myVtkStringMacro
that declared the methods as "const".  Custom macros like this
are bad for several reasons.

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