Unclear license for environment maps

## How can Bevy's documentation be improved?

The Pisa environment map in our test assets was generated from a references in https://github.com/KhronosGroup/glTF-Sample-Environments, which
- Does not include licenses: https://github.com/KhronosGroup/glTF-Sample-Environments/issues/5
- Links a dead link as the source for the Pisa files: https://gl.ict.usc.edu/data/highresprobes/

archive.org has the link indexed: https://web.archive.org/web/20190516111811/https://gl.ict.usc.edu/data/highresprobes/, but there is also no licensing information there:
> In 2001, we released a gallery of light probe images including images of Grace Cathedral, the Eucalyptus Grove, and St Paul's Bascillica. Most of these probes were assembled using mirrored ball images. As digital cameras have advanced, it is now possible to create higher resolution light probes. On this page, we have release several such probes that we have since created.

I assume this is alright-ish in practice, since we are using them in good faith as Khronos distributes them as samples. But it seems to me that the license for this file is completely unknown, implying that all copyright is reserved and distribution is not permitted?