create_normals_split, calc_normals_split, and free_normals_split are removed, and are replaced by the simpler Mesh.corner_normals collection property. Since it gives access to the normals cache, it is automatically updated when relevant data changes.
Source: https://developer.blender.org/docs/release_notes/4.1/python_api/
Personally, I'm not in a hurry to fix this though, as I don't use MD3 anymore, and even if I do -- I'm still clinging on to Blender 2.79. :P
Just putting this ticket here to say, basically, "I know"