template: rename get_vertebral_level_from_slice param
template: rename get_vertebral_level_from_slice param

Former-commit-id: 3f1d3388337c5ec30d9a79911dbd893a365ad93a
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox