PyUnicode_AsUTF8String(): /F picks up what I missed: the local var

`str' is no longer necessary.  Gotta turn on -Wall!

Objects/unicodeobject.c

@@ -901,8 +901,6 @@ PyObject *PyUnicode_EncodeUTF8(const Py_UNICODE *s,
 
 PyObject *PyUnicode_AsUTF8String(PyObject *unicode)
 {
-    PyObject *str;
-    
     if (!PyUnicode_Check(unicode)) {
         PyErr_BadArgument();
         return NULL;