simulation: improve equivalence testers explanations messages (part 2)

Default values for tested_property and tested_property_title must not
be of type tuple any more since theses properties are no longer multi
valued

product/ERP5/bootstrap/erp5_property_sheets/PropertySheetTemplateItem/portal_property_sheets/EquivalenceTester/tested_property_property.xml

@@ -27,7 +27,7 @@
             <key> <string>categories</string> </key>
             <value>
               <tuple>
-                <string>elementary_type/lines</string>
+                <string>elementary_type/string</string>
               </tuple>
             </value>
         </item>
@@ -49,7 +49,7 @@
         </item>
         <item>
             <key> <string>property_default</string> </key>
-            <value> <string>python: ()</string> </value>
+            <value> <string>python: None</string> </value>
         </item>
       </dictionary>
     </pickle>

product/ERP5/bootstrap/erp5_property_sheets/PropertySheetTemplateItem/portal_property_sheets/EquivalenceTester/tested_property_title_property.xml

@@ -49,7 +49,7 @@
         </item>
         <item>
             <key> <string>property_default</string> </key>
-            <value> <string>python: ()</string> </value>
+            <value> <string>python: None</string> </value>
         </item>
         <item>
             <key> <string>translatable</string> </key>