ref(gitignore): clean up old ignores, remove os-specific files

files to be ignored like .DS_Store on OSX should exist in a global
.gitignore file, where it is ignored across all repositories.

See https://help.github.com/articles/ignoring-files/#create-a-global-gitignore
Ah, yes it does. I didn't have a local cluster and didn't have a `.vagrant/` dir. You could argue this should be a global .gitignore entry as well, but we should add it back in to ours I think.