Fix refleaks in test_unicode and test_string related to the new format code.

Stop polluting namespace.

Include/unicodeobject.h

@@ -1437,10 +1437,8 @@ PyAPI_FUNC(Py_UNICODE*) Py_UNICODE_strchr(
     const Py_UNICODE *s, Py_UNICODE c
     );
 
-PyObject *
-_unicodeformatter_iterator(PyObject *str);
-PyObject *
-_unicodeformatter_field_name_split(PyObject *field_name);
+PyObject *_PyUnicode_FormatterIterator(PyObject *str);
+PyObject *_PyUnicode_FormatterFieldNameSplit(PyObject *field_name);
 
 #ifdef __cplusplus
 }