Message 403926 - Python tracker

(This follows bpo-45211.)

In gh-28586 I added the code in Py_SetPythonHome() to set _Py_path_config.stdlib_dir to the provided directory.  However, this is the wrong value.  Furthermore, the relationship between _Py_path_config.home and _Py_path_config.stdlib_dir is meant to managed in Modules/getpath.c (and PC/getpathp.c).  So the code setting _Py_path_config.stdlib_dir in Py_SetPythonHome() should be dropped.