Remove unused s3fs dependency

[ggilder]

I noticed that it takes quite a while to download the various dependencies of s3fs during pip install, and it appears that s3fs is not actually referenced anywhere in the repo (see search). So no need to include in setup.py.

[ggilder]

For more context - doing pip install stable-audio-tools takes a long time downloading multiple versions of s3fs as well as its dependencies like boto3, botocore and aiobotocore, with messages like:

INFO: pip is looking at multiple versions of s3fs to determine which version is compatible with other requirements. This could take a while.

[ggilder]

@zqevans any opposition to this?

[akx]

#139 is related.