Removes brew-cask install step, as it is deprecated

This change fixes the maximum-awesome installation failure due to being unable to install Homebrew-cask (error message 'No available formula with the name 'brew-cask"').

As of December 2015, "brew install brew-cask" is deprecated in favor of keeping Homebrew-cask up-to-date together with Homebrew. For details, see:

https://github.com/ctran/homebrew-cask#important-december-2015-update-homebrew-cask-will-now-be-kept-up-to-date-together-with-homebrew-see-15381-for-details-if-you-havent-yet-run-brew-uninstall---force-brew-cask-brew-update-to-switch-to-the-new-system

TESTED=Confirmed that maximum-awesome install process works as expected with the proposed changes.