Remove Formulae for Docker and Boot2Docker

The [official installation instructions](https://docs.docker.com/installation/mac/) for Docker now point to using the [OSX Installer](https://github.com/boot2docker/osx-installer/releases) which is a .pkg installation utility. This one installer installs the Boot2Docker CLI as well as a running Docker VM. Because this official installation channel is so convenient, I wanted to start this conversation here: should these two formulae now be removed or, at the least, moved to something like [homebrew/homebrew-binary](https://github.com/Homebrew/homebrew-binary)?

Relevant: #29961 and dotcloud/docker#6256

Signed-off-by: David Celis <me@davidcel.is>