https://github.com/jlund/streisand/blob/master/playbooks/str...
Comment out any roles you don't want with a # at the beginning of the line, YAML is very picky about syntax.
comment edit: Think of roles in ansible like building blocks or common chores you can apply to any server. It might be nice to not have so much stuff by default, but this tool isn't meant for complete technical novices, so it is expected (in my opinion) that you go in and prune anything out you don't want/need. What is nice is that you have lots of options and if you ever need to add a role you can just uncomment it and re-run the playbook.
Lately I've been using this as a way to quickly apply selective config. It feels 'hacked-on', but it works.