bpo-37878: PyThreadState_DeleteCurrent() was not removed (GH-20489)

Update What's New in Python 3.9.

PyThreadState_DeleteCurrent was not removed, but excluded from the limited C API.
diff --git a/Doc/whatsnew/3.9.rst b/Doc/whatsnew/3.9.rst
index 35496d7..a42ec09 100644
--- a/Doc/whatsnew/3.9.rst
+++ b/Doc/whatsnew/3.9.rst
@@ -829,9 +829,6 @@
   removed, standard :class:`bytes` objects are always used instead.
   (Contributed by Jon Janzen in :issue:`36409`.)
 
-* The C function ``PyThreadState_DeleteCurrent()`` has been removed. It was not documented.
-  (Contributed by Joannah Nanjekye in :issue:`37878`.)
-
 * The C function ``PyGen_NeedsFinalizing`` has been removed. It was not
   documented, tested, or used anywhere within CPython after the implementation
   of :pep:`442`. Patch by Joannah Nanjekye.
@@ -1108,6 +1105,8 @@
 
   * Exclude the following functions from the limited C API:
 
+    * ``PyThreadState_DeleteCurrent()``
+      (Contributed by Joannah Nanjekye in :issue:`37878`.)
     * ``_Py_CheckRecursionLimit``
     * ``_Py_NewReference()``
     * ``_Py_ForgetReference()``