sct_label_utils: changed action={'remove','keep'} to action
sct_label_utils: changed action={'remove','keep'} to action


Former-commit-id: b44f4aada698506532185d6dbdf7efddb9e52553
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox