bpo-43270: Remove private _PyErr_OCCURRED() macro (GH-24579)

Remove the private _PyErr_OCCURRED() macro: use the public
PyErr_Occurred() function instead.

CPython internals must use the internal _PyErr_Occurred(tstate)
function instead: it is the most efficient way to check if an
exception was raised.
diff --git a/Python/ceval.c b/Python/ceval.c
index 81a21c9..4771a51 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -2750,7 +2750,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, PyFrameObject *f, int throwflag)
                                        (PyDictObject *)f->f_builtins,
                                        name);
                 if (v == NULL) {
-                    if (!_PyErr_OCCURRED()) {
+                    if (!_PyErr_Occurred(tstate)) {
                         /* _PyDict_LoadGlobal() returns NULL without raising
                          * an exception if the key doesn't exist */
                         format_exc_check_arg(tstate, PyExc_NameError,