bpo-36346: Undeprecate private function _PyUnicode_AsUnicode(). (GH-21336)

diff --git a/Include/cpython/unicodeobject.h b/Include/cpython/unicodeobject.h
index a82eee4..49ad32d 100644
--- a/Include/cpython/unicodeobject.h
+++ b/Include/cpython/unicodeobject.h
@@ -581,7 +581,7 @@
 
 /* Similar to PyUnicode_AsUnicode(), but raises a ValueError if the string
    contains null characters. */
-Py_DEPRECATED(3.3) PyAPI_FUNC(const Py_UNICODE *) _PyUnicode_AsUnicode(
+PyAPI_FUNC(const Py_UNICODE *) _PyUnicode_AsUnicode(
     PyObject *unicode           /* Unicode object */
     );