Turn off smtk-discrete-moab-reader by default
DSMTK_ENABLE_MOAB_DISCRETE_READER should be off by default because vtkCmbMoabReader in discrete session may only be needed for debugging purpose
DSMTK_ENABLE_MOAB_DISCRETE_READER should be off by default because vtkCmbMoabReader in discrete session may only be needed for debugging purpose