Remove entire bus route at once

I'm assuming you want to delete all the route relations that belong to a single route master relation ? Deleting the highway=* ways that are members of the route relation is not a good idea.

With JOSM, you can do the former by selecting any highway that is part of the route, then right-click on the route master relation in the tag/membership panel and choose select members, and finally press delete. You can then delete the route master relation itself. Not sure how to do this with other editors.

That said, I would probably not bulk-delete things like this: route relations can be a bit complex and I'd prefer to check relations individually before deleting each one. Route master relations don't usually have too many members.