[3.13] Doc: C API: PyThreadState::on_delete was removed in v3.13 (GH-126536) (#127053)

Doc: C API: `PyThreadState::on_delete` was removed in v3.13 (GH-126536)
(cherry picked from commit 9bca3ef)

Co-authored-by: Richard Hansen <rhansen@rhansen.org>

Author: miss-islington

Doc/c-api/init.rst

@@ -1332,6 +1332,9 @@ All of the following functions must be called after :c:func:`Py_Initialize`.
       This function now calls the :c:member:`PyThreadState.on_delete` callback.
       Previously, that happened in :c:func:`PyThreadState_Delete`.
 
+   .. versionchanged:: 3.13
+      The :c:member:`PyThreadState.on_delete` callback was removed.
+
 
 .. c:function:: void PyThreadState_Delete(PyThreadState *tstate)