Reasoning: even though the model content of these files is BSD compatible, they carry a Autodesk Copyright Notice after being converted to FBX. I have serious doubts that this could serve as base for claims against us, but better safe than sorry.
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These models are not generally redistributable under the terms of Assimp's BSD license. Usually, an additional requirement on the use of the data is imposed (i.e. no commercial use, need credits, some creative commons variants, ...).
So, if you re-package Assimp for use in a 'clean' OSS package, consider removing this directory.