README: Remove slowstart instructions. (#3810)
README: Remove slowstart instructions. (#3810)

None of the development team use this approach to running a dev env. It
no longer works without modifying `test/startservers.py` and the `test/`
configurations. Given that it has been broken for a month+ and has only
provoked one user issue I think we can be fairly confident that few others
are using this method of setting up a Boulder development environment
and should prioritize our time/docs accordingly.
jcjones/boulder,jcjones/boulder,jfrazelle/boulder,letsencrypt/boulder,lucasallan/boulder,lucasallan/boulder,jsha/boulder,bmw/boulder,bmw/boulder,jcjones/boulder,letsencrypt/boulder,jfrazelle/boulder,lucasallan/boulder,jsha/boulder,jfrazelle/boulder,jsha/boulder,bmw/boulder,jfrazelle/boulder,jcjones/boulder,letsencrypt/boulder