Either document how to setup git-lfs, or get rid of it

[dellard]

The example test output files are represented in the git repo by references to git lfs objects. It doesn't look like this dependency is mentioned anywhere (or at least not blatantly enough to catch my eye), so my builds were failing.

I don't like adding dependencies (especially ones that aren't compatible with some platforms), and I don't know that we're benefitting from using git-lfs here anyway. I would recommend either getting rid of it (if that's possible), or at minimum adding documentation to the README.md explaining how to acquire, install, and use git-lfs correctly.