Remove `--runname` option (and machinery)
As highlighted in a Mattermost discussion with Alex Grecu, rivet
still features the --runname
option, and the underlying machinery for prepending a "top-level directory" to histogram paths, despite the motivation for that feature being lost in the dark, and AIDA-flavoured past. We can't think of a reason for it anymore, and Alex (and maybe others) had an impression of its purpose that was quite unhelpful in practice. Time to remove.