Bumping versions to 16.4.1. (#597)

Listable 16.4.1.

I've also removed the links in the CHANGELOG.md (as discussed during
work-sesh) and updated related docs.

### Checklist

- Post-merge: Tag the release
```
./Scripts/tag_release.sh 16.4.1 <merge commit SHA>
```

Author: robmaceachern