investigate and transition built-in osx_defaults

[mroth]

With ansible 2.0, it looks like osx_defaults is now in default modules, so investigate migrating to that instead of my vendored fork.

Need to note this issue, which looks like it was only fixed when 2.3 releases: https://github.com/ansible/ansible/commit/5536ffe9784c429951f8a11185921c6316beb80d