v4: navbar-form removed, but still in documentation

Created by: davidjb

I've been testing v4 and noticed that the documentation and examples in the v4-dev branch (https://github.com/twbs/bootstrap/blob/v4-dev/docs/components/navbar.md) mention .navbar-form, but the class was removed in this commit: https://github.com/twbs/bootstrap/commit/d6b6a20a0daaed70ec6f395dd813ea460b394e6c#diff-df1f74faf207a474f1d78c86393221c8L162

Is this documentation no longer needed / an entry needed for the Migration documentation?