ERP5Catalog: Remove useless object class declaration in __init__

As pointed by /Jerome, it is only used for ZMI classes
nexedi/erp5@557c20bd (comment 52113)

product/ERP5Catalog/__init__.py

@@ -38,9 +38,9 @@ document_classes = updateGlobals( this_module, globals(), permissions_module = P
 
 # Define object classes and tools
 from Tool import ArchiveTool, ERP5CatalogTool
-from Document import ERP5Catalog
+
 import CatalogTool
-object_classes = (ERP5Catalog.ERP5Catalog,)
+object_classes = ()
 portal_tools = (CatalogTool.CatalogTool,
                 ERP5CatalogTool.ERP5CatalogTool,
                 ArchiveTool.ArchiveTool)