Fix the remaining issues with the StatementElement.next refactoring.

test/test_regression.py

@@ -104,7 +104,7 @@ class TestRegression(TestCase):
         parser = Parser(s)
         for i, s in enumerate(parser.module.statements, 3):
             for c in s.expression_list():
-                self.assertEqual(c.execution.end_pos[1], i)
+                self.assertEqual(c.next.end_pos[1], i)
 
     def check_definition_by_marker(self, source, after_cursor, names):
         r"""