This is part of the NServiceBus Upgrade Guide from Version 4 to 5, which also includes the following individual upgrade guides for specific components:
Hosting
Roles are obsolete
In NServiceBus.Host version 5 and above, roles are obsolete and should not be used. The functionality of AsA_Server, and AsA_Publisher is now the default and can be safely removed. Read the Host guidance on alternatives for using roles.