Removing the test of Element that causes ref-leak in GC (issue #14464).

I will now continue investigating the cause of the ref-leak, but I wanted
to remove the test so that the refcount test in the buildbots could be clean.
The whole change (adding GC to Element) is not reverted because it improved
the situation (GC works for immediate cycles) and didn't cause regressions
(the test is new and was added together with the fix).

Lib/test/test_xml_etree.py

@@ -1859,16 +1859,6 @@ class BasicElementTest(unittest.TestCase):
         gc_collect()
         self.assertIsNone(wref())
 
-        # A longer cycle: d->e->e2->d
-        e = ET.Element('joe')
-        d = Dummy()
-        d.dummyref = e
-        wref = weakref.ref(d)
-        e2 = ET.SubElement(e, 'foo', attr=d)
-        del d, e, e2
-        gc_collect()
-        self.assertIsNone(wref())
-
 
 class ElementTreeTest(unittest.TestCase):
     def test_istype(self):