disable psiturk-heroku-config default creation of psql db
The currently-undocumented psiturk-heroku-config command no longer attaches a postgresql addon by default. I'm calling this just a bugfix because (1) the docs assume that it doesn't attach the psql database, and (2) that command isn't even documented anyway. Will version-feature-bump when this feature is better thought through.
Disabling because I think this will overall make the transition to v3 smoother.