How to skip the tools during installation which I don't want to install from this automated installation list for osx dev tools?
Comment out the four lines that reference Heroku by adding the pound/hash sign in front of each one, like so:

# fancy_echo "Installing Heroku CLI client ..."
  # brew_install_or_upgrade 'heroku-toolbelt'

# fancy_echo "Installing the heroku-config plugin to pull config variables locally to be used as ENV variables ..."
  # heroku plugins:install https://github.com/ddollar/heroku-config.git