Revert "XXX partial reversion of 1cbe460"

This reverts commit 40f9873.

Author: skirpichev

Lib/test/test_class.py

@@ -449,7 +449,6 @@ def __delattr__(self, *args):
 
     def testHasAttrString(self):
         import sys
-        from test.support import import_helper
         _testlimitedcapi = import_helper.import_module('_testlimitedcapi')
 
         class A:
@@ -1014,11 +1013,8 @@ class C:
         C.a = X()
         C.a = X()
 
-    @cpython_only
+    @support.nomemtest
     def test_detach_materialized_dict_no_memory(self):
-        # Skip test if _testcapi is not available:
-        import_helper.import_module('_testcapi')
-
         code = """if 1:
             import test.support
             import _testcapi