test__greenlet.py: fix TestStuff.test_wait_error

It failed because it depended on order in which greenlets spawned in the same iteration are executed.
With libevent, the order used to be the same as spawn() calls. With libev, the order is reversed.

greentest/test__greenlet.py

@@ -381,15 +381,11 @@ class TestStuff(greentest.TestCase):
             sleep(DELAY)
             return 1
         x = gevent.spawn(x)
-        z = gevent.spawn(lambda: 3)
         y = gevent.spawn(lambda: getcurrent().throw(ExpectedError('test_wait_error')))
-        y.link(x)
         x.link(y)
-        y.link(z)
-        z.link(y)
-        self.assertRaises(ExpectedError, gevent.joinall, [x, y, z], raise_error=True)
+        y.link(x)
+        self.assertRaises(ExpectedError, gevent.joinall, [x, y], raise_error=True)
         self.assertRaises(greenlet.LinkedFailed, gevent.joinall, [x], raise_error=True)
-        self.assertEqual(z.get(), 3)
         self.assertRaises(ExpectedError, gevent.joinall, [y], raise_error=True)
 
     def test_joinall_exception_order(self):