Issue #22413: Remove comment made out of date by Argument Clinic

Modules/_io/stringio.c

@@ -696,10 +696,8 @@ _io_StringIO___init___impl(stringio *self, PyObject *value,
     char *newline = "\n";
     Py_ssize_t value_len;
 
-    /* Parse the newline argument. This used to be done with the 'z'
-       specifier, however this allowed any object with the buffer interface to
-       be converted. Thus we have to parse it manually since we only want to
-       allow unicode objects or None. */
+    /* Parse the newline argument. We only want to allow unicode objects or
+       None. */
     if (newline_obj == Py_None) {
         newline = NULL;
     }