Update logging.rst

Update to include changes proposed in issue #794

docs/writing/logging.rst

@@ -55,17 +55,8 @@ this in your ``__init__.py``
 
 .. code-block:: python
 
-    # Set default logging handler to avoid "No handler found" warnings.
     import logging
-    try:  # Python 2.7+
-        from logging import NullHandler
-    except ImportError:
-        class NullHandler(logging.Handler):
-            def emit(self, record):
-                pass
-
-    logging.getLogger(__name__).addHandler(NullHandler())
-
+    logging.getLogger(__name__).addHandler(logging.NullHandler())
 
 
 Logging in an Application