Header: Remove forcing transform to be rigid-body
Header: Remove forcing transform to be rigid-body

Reverts part of 522a798b.

MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3