Interp::Base: Remove check_3D_nonunity()
Interp::Base: Remove check_3D_nonunity()

Although this is a reasonable check when performing image processing involving interpolation, it prevents loading such images in mrview, where they can in fact be displayed reasonably.
Check was originally introduced in #1017.

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