REF: straighten_spinalcord: removed flag -cpu-nb (don't need it anymore)
REF: straighten_spinalcord: removed flag -cpu-nb (don't need it anymore)

Former-commit-id: ef70b51131926c2bd061770f6ad0d356a3a3fa57
Former-commit-id: e03e5112d103c640fe1827dfeda747832e473957
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox