gh-106023: Update What's New in 3.13: _PyObject_FastCall() (#117633)

The function _PyObject_FastCall() was restored.

Author: vstinner

Doc/whatsnew/3.13.rst

@@ -2006,11 +2006,6 @@ Removed
 
   (Contributed by Victor Stinner in :gh:`105182`.)
 
-* Remove private ``_PyObject_FastCall()`` function:
-  use ``PyObject_Vectorcall()`` which is available since Python 3.8
-  (:pep:`590`).
-  (Contributed by Victor Stinner in :gh:`106023`.)
-
 * Remove ``cpython/pytime.h`` header file: it only contained private functions.
   (Contributed by Victor Stinner in :gh:`106316`.)