Exclude default roles from custom_permissions

It makes no sense to duplicate a role that can access everything,
and another that shouldn't access anything.

core/app/models/spree/permission_set.rb

@@ -13,6 +13,7 @@ class PermissionSet < Spree::Base
     scope :custom_permissions, -> {
       where.not(id: display_permissions)
       .where.not(id: management_permissions)
+      .where.not(set: ['Spree::PermissionSets::SuperUser', 'Spree::PermissionSets::DefaultCustomer'])
     }
   end
 end