Bug 1652557: don't skip test_bug767684.html when xorigin iframes and fission are enabled. r=masayuki

The test failed neither locally nor on try, hence enabling it again.

Differential Revision: https://phabricator.services.mozilla.com/D86706

editor/libeditor/tests/mochitest.ini

@@ -142,7 +142,6 @@ skip-if = headless
 [test_bug757371.html]
 [test_bug757771.html]
 [test_bug767684.html]
-skip-if = (xorigin && fission) # application crashed [@ std::_Function_handler<void (bool&&), mozilla::dom::CanonicalBrowsingContext::PendingRemotenessChange::Complete(mozilla::dom::ContentParent*)::$_12>::_M_invoke(std::_Any_data const&, bool&&)]
 [test_bug772796.html]
 [test_bug773262.html]
 [test_bug780035.html]