Backout d2c1521ad0a1: _Py_IDENTIFIER() uses UTF-8 again

Objects/unicodeobject.c

@@ -1744,8 +1744,9 @@ PyObject *
 _PyUnicode_FromId(_Py_Identifier *id)
 {
     if (!id->object) {
-        id->object = unicode_fromascii((unsigned char*)id->string,
-                                       strlen(id->string));
+        id->object = PyUnicode_DecodeUTF8Stateful(id->string,
+                                                  strlen(id->string),
+                                                  NULL, NULL);
         if (!id->object)
             return NULL;
         PyUnicode_InternInPlace(&id->object);