Added bibliography reference for sct_denoising_onlm (#3425)
Added bibliography reference for sct_denoising_onlm (#3425)

* Removed unused import

* Moved import at the top

* Added reference for non-local means denoising
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox