Remove old tests that have been migrated to the v8 repo.

LayoutTests/fast/js/script-tests/object-extra-comma.js

-description(
-    'This test checks some object construction cases, including ' +
-    '<a href="https://bugs.webkit.org/show_bug.cgi?id=5939">5939: final comma in javascript object prevents parsing</a>' +
-    '.');
-
-shouldBe("var foo = { 'bar' : 'YES' }; foo.bar", "'YES'");
-shouldBe("var foo = { 'bar' : 'YES', }; foo.bar", "'YES'");
-shouldBe("var foo = { 'bar' : 'YES' , }; foo.bar", "'YES'");
-shouldThrow("var foo = { , 'bar' : 'YES' }; foo.bar");
-shouldThrow("var foo = { 'bar' : 'YES',, }; foo.bar");