Remove built files from git

[ockham]

Do we have to check built files into git? I just filed a PR (#84) to remove an obsolete logo, and it was really hard to tell which files I needed to remove manually. Just removing what I thought was the 'source of truth' (in sources/svg/) didn't cut itm, nor did re-running the build afterwards.

Ideally, built files should only be included with the published npm, but not in the git repo IMO.