Remove `$` from `node_id` KeyValue in the Bandwidth File

This would easy PostgreSQL queries using the new metrics DB, because most (or all) of the other tables/file descriptors don't use anymore the $ in the fingerprint field.

It could be a problem though for other tools cause this is a major change. It seems that it isn't a problem for the metrics library or the new descriptors parser because they just get what there's inside node_id without checking it. We should check.