bpo-20443: Update What's New In Python 3.9 (GH-17986)

The sys.argv[0] change has been reverted.

Author: vstinner

Doc/whatsnew/3.9.rst

@@ -83,7 +83,7 @@ Other Language Changes
 
 * Python now gets the absolute path of the script filename specified on
   the command line (ex: ``python3 script.py``): the ``__file__`` attribute of
-  the :mod:`__main__` module, ``sys.argv[0]`` and ``sys.path[0]`` become an
+  the :mod:`__main__` module and ``sys.path[0]`` become an
   absolute path, rather than a relative path. These paths now remain valid
   after the current directory is changed by :func:`os.chdir`. As a side effect,
   a traceback also displays the absolute path for :mod:`__main__` module frames