ERP5Workflow: remove useless storage id in properties from Variable property sheet

product/ERP5/bootstrap/erp5_property_sheets/PropertySheetTemplateItem/portal_property_sheets/Variable/variable_expression_property.xml

@@ -30,7 +30,9 @@
         </item>
         <item>
             <key> <string>storage_id</string> </key>
-            <value> <string>variable_expression</string> </value>
+            <value>
+              <none/>
+            </value>
         </item>
       </dictionary>
     </pickle>

product/ERP5/bootstrap/erp5_property_sheets/PropertySheetTemplateItem/portal_property_sheets/Variable/variable_value_property.xml

@@ -55,7 +55,9 @@
         </item>
         <item>
             <key> <string>storage_id</string> </key>
-            <value> <string>variable_value</string> </value>
+            <value>
+              <none/>
+            </value>
         </item>
       </dictionary>
     </pickle>