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 Cask?

Relevant: #29961 and dotcloud/docker#6256

Signed-off-by: David Celis <me@davidcel.is>