remove `clean-fid`

[space-pope]

The clean-fid library has an old version of requests pinned in its dependencies that's currently causing me some headaches.

I see a couple discussions related to replacing/reimplementing clean-fid (#7 and #8), and I don't see any imports related to it in the current code, so I was wondering if you'd be open to removing it from the requirements file for the next release. Feel free to close this if not; just thought I'd check.

Thanks!