don't use ScalableSelectorMixIn with DevpollSelector tests

The amount of descriptors returned with select is not affected by FD_SETSIZE or RLIMIT_NOFILE when using devpoll - the limit is hardcoded to 1024 now.

Author: kulikjak

Lib/test/test_selectors.py

@@ -603,8 +603,7 @@ def test_empty_select_timeout(self):
 
 @unittest.skipUnless(hasattr(selectors, 'DevpollSelector'),
                      "Test needs selectors.DevpollSelector")
-class DevpollSelectorTestCase(BaseSelectorTestCase, ScalableSelectorMixIn,
-                              unittest.TestCase):
+class DevpollSelectorTestCase(BaseSelectorTestCase, unittest.TestCase):
 
     SELECTOR = getattr(selectors, 'DevpollSelector', None)