test_result: remove button to hide expected failures from Zelenium tests

ERP5 now produces the results with `<details>` HTML elements, so this
hack is no longer necessary. It was anyway not working at all on ERP5JS
and not working well on erp5_xhtml_style

bt5/erp5_test_result/SkinTemplateItem/portal_skins/erp5_test_result/TestResultLine_view.xml

@@ -96,7 +96,6 @@
                         <string>my_duration</string>
                         <string>my_parent_int_index</string>
                         <string>my_source_title</string>
-                        <string>your_hide_expected_failure</string>
                       </list>
                     </value>
                 </item>