erp5_simulation: remove default sort from listbox of portal_simulation

this 'relative_url | ascending' sort can lead to killer queries and it is of no use

bt5/erp5_simulation/SkinTemplateItem/portal_skins/erp5_simulation/SimulationTool_viewContentList/listbox.xml

@@ -627,12 +627,7 @@
                 <item>
                     <key> <string>sort</string> </key>
                     <value>
-                      <list>
-                        <tuple>
-                          <string>relative_url</string>
-                          <string>ascending</string>
-                        </tuple>
-                      </list>
+                      <list/>
                     </value>
                 </item>
                 <item>