“Unlinked kegs in your Cellar”. How do I remove them?

Question

After installing and uninstalling some programs through brew and brew cask, now I get brew doctor saying \"unlinked kegs in your Cellar\".

Answer 1

2018 Update

$ brew link --help
    If --overwrite is passed, Homebrew will delete files which already exist
    in the prefix while linking.
$ brew link --overwrite [package]
$ brew doctor