straighten_spinalcord: re-enabled hanning filter
straighten_spinalcord: re-enabled hanning filter

Fixes #2032


Former-commit-id: 6dcf5d64605f205a1bb91f82ac37183c7fb98b90
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox