COMP:  DTIPrep builds against ITKv4 now.
COMP:  DTIPrep builds against ITKv4 now.

Remove unnecessary (and fragile logic) regarding ITKv3
build options.

NIRALUser/DTIPrep,retfurger/alpha,retfurger/alpha,retfurger/alpha,juanprietob/DTIPrep,juanprietob/DTIPrep,NIRALUser/DTIPrep