Rm prettyprint

prettyprint was added in [https://github.com/mozilla/scanjs/commit/b4ca903fb9546cd623481aa1aa6a7d20388f6dc0](https://github.com/mozilla/scanjs/commit/b4ca903fb9546cd623481aa1aa6a7d20388f6dc0) but never really used. It was already partially removed in #35

If we really want prettyprinting (#45) we should do it differently..