There are several BindingMappings for system roles that exist in stage but have no assigned users/groups. It is unclear how this came to be, but there are no such BindingMappings in production, so perhaps it was a transient bug that never hit prod. 

This isn't in and of itself problematic, but these BindingMappings also do not have equivalent RoleBindings because they would never be hit by the binding scope migration. This means that, after this PR, the local models would show relations that do not exist in Relations. This would cause problems if a subject was ever assigned to the binding in the future.