This is part of the NServiceBus Upgrade Guide from Version 7 to 8, which also includes the following individual upgrade guides for specific components:
Starting with NServiceBus.RavenDB version 6.2.0, the built-in gateway API is obsolete and using it will produce the following message:
RavenDB gateway persistence has been moved to the NServiceBus.Gateway.RavenDB dedicated package. Will be treated as an error from version 7.0.0. Will be removed in version 8.0.0.
To migrate to the new gateway API: