Removed -fobjc-gc from VTK_REQUIRED_OBJCXX_FLAGS
Removed -fobjc-gc from VTK_REQUIRED_OBJCXX_FLAGS

There are 3 memory management models in Cocoa,
chronologically by introduction: MRR, GC, ARC.
VTK supports the first two.
GC is now deprecated however, and Xcode 5.1 will
no longer even build GC code.  Therefore
removed the -fobjc-gc option as a default.
(It built the libraries as both MRR and GC
compatible, which was convienent for library code.)

Change-Id: I5f0ee437402bbcbbb20f2088f56298adf3a34d6e

gram526/VTK,sankhesh/VTK,msmolens/VTK,jmerkow/VTK,demarle/VTK,mspark93/VTK,ashray/VTK-EVM,SimVascular/VTK,sumedhasingla/VTK,jmerkow/VTK,sankhesh/VTK,SimVascular/VTK,SimVascular/VTK,sumedhasingla/VTK,SimVascular/VTK,johnkit/vtk-dev,berendkleinhaneveld/VTK,ashray/VTK-EVM,berendkleinhaneveld/VTK,msmolens/VTK,hendradarwin/VTK,sumedhasingla/VTK,demarle/VTK,candy7393/VTK,mspark93/VTK,candy7393/VTK,msmolens/VTK,jmerkow/VTK,jmerkow/VTK,hendradarwin/VTK,gram526/VTK,msmolens/VTK,ashray/VTK-EVM,msmolens/VTK,ashray/VTK-EVM,hendradarwin/VTK,SimVascular/VTK,sumedhasingla/VTK,candy7393/VTK,sankhesh/VTK,gram526/VTK,sankhesh/VTK,gram526/VTK,demarle/VTK,keithroe/vtkoptix,sumedhasingla/VTK,johnkit/vtk-dev,sankhesh/VTK,jmerkow/VTK,mspark93/VTK,keithroe/vtkoptix,mspark93/VTK,jmerkow/VTK,johnkit/vtk-dev,ashray/VTK-EVM,keithroe/vtkoptix,msmolens/VTK,mspark93/VTK,candy7393/VTK,sumedhasingla/VTK,mspark93/VTK,keithroe/vtkoptix,msmolens/VTK,demarle/VTK,ashray/VTK-EVM,keithroe/vtkoptix,gram526/VTK,SimVascular/VTK,johnkit/vtk-dev,berendkleinhaneveld/VTK,jmerkow/VTK,hendradarwin/VTK,keithroe/vtkoptix,demarle/VTK,johnkit/vtk-dev,keithroe/vtkoptix,candy7393/VTK,mspark93/VTK,demarle/VTK,berendkleinhaneveld/VTK,berendkleinhaneveld/VTK,SimVascular/VTK,gram526/VTK,sankhesh/VTK,hendradarwin/VTK,ashray/VTK-EVM,sumedhasingla/VTK,johnkit/vtk-dev,jmerkow/VTK,berendkleinhaneveld/VTK,sumedhasingla/VTK,hendradarwin/VTK,candy7393/VTK,demarle/VTK,gram526/VTK,hendradarwin/VTK,sankhesh/VTK,keithroe/vtkoptix,berendkleinhaneveld/VTK,SimVascular/VTK,candy7393/VTK,mspark93/VTK,johnkit/vtk-dev,demarle/VTK,gram526/VTK,candy7393/VTK,sankhesh/VTK,msmolens/VTK,ashray/VTK-EVM