Follow-up to #184 (comment). In short, this is not being maintained, and has opinions that are not shared across TTS, so let's drastically reduce its scope. My proposal of what should remain in scope, either in the script itself or as documentation (pointing to canonical instructions).

• XCode command-line tools
• Homebrew
• git-seekrets, or a suitable equivalent (Use a maintained tool for preventing checking secrets into version control #185). It's 18F policy - the spirit of it is that we protect ourselves from accidentally committing secrets is still very valid.
• Git configuration

• Delete the rest from the repository