ERP5Type/patches: prepare for removal of Products.DCWorkflowGraph

Supports the case where Products.DCWorkflowGraph is not present.
Even though we are removing Products.DCWorkflowGraph from the
software release, we don't remove this monkey patch yet, because
this monkey patch also fixed a severe security issue. We keep the
patch for the cases where a recent ERP5 runs on an old SlapOS where
the product is still there.

This change just moves the existing code in a try/except ImportError
block

product/ERP5Type/ZopePatch.py

@@ -85,9 +85,7 @@ from Products.ERP5Type.patches import zopecontenttype
 from Products.ERP5Type.patches import OFSImage
 from Products.ERP5Type.patches import _transaction
 from Products.ERP5Type.patches import default_zpublisher_encoding
-if six.PY2:
-  # DCWorkflowGraph is dead since 2011, so no py3 version
-  from Products.ERP5Type.patches import DCWorkflowGraph
+from Products.ERP5Type.patches import DCWorkflowGraph
 from Products.ERP5Type.patches import SourceCodeEditorZMI
 from Products.ERP5Type.patches import CachingPolicyManager
 from Products.ERP5Type.patches import AcceleratedHTTPCacheManager