cleanup RemoveArray implementations in vtkFieldData and vtkDataSetAttributes
vtkFieldData::RemoveArray(int index) to the public interface, as it already is in
vtkDataSetAttributes (since 64d06316).
I couldn't see a reason why access to
RemoveArray(int) should be different between vtkFieldData and vtkDataSetAttributes. Is there a reason not to use this function in client code and instead stick to
RemoveArray(const char *name)?
Besides, this replaces the duplicated implementation of
vtkDataSetAttributes::RemoveArray(const char *name) by a
using declaration (I hope this is supported by relevant compilers). Also, the implementation in
vtkFieldData is moved to the cxx file, as is was in
vtkDataSetAttributes since c5b4805a.