BUG: label_utils: fixed bug with "remove"
BUG: label_utils: fixed bug with "remove"

Former-commit-id: 3619cacff6658756d413fb4ee64d5ad48df2ce83
Former-commit-id: a4e218bfd56355ca9fd99e34d7a539d505b1dc21
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox