Formerly, the "launch a chutney network" code was duplicated in
"setup" and "arti-bench", since "setup" always launched an arti
proxy, while "arti-bench" didn't want that functionality.
Now the "setup" script launches an arti proxy conditionally,
depending on whether the "proxy" argument is given.
As per #309
Update all references. There is one remaining hit for
git-grep '\.sh\b'
namely "build.sh" in maint/reproducible_build, which I think is
the build script for osxcross - ie, an external project.