This code was changed in ea196490a0 to validate that `--config` wasn't passed along with other flags. Unfortunately, the implementation was checking `PersistentFlags()`, which was not parsed at the point it was being validated. The result was that `--config` was _always_ rejected, not just when it was specified alongside other flags.
The fix is to use `Flags()` instead, which contains the expected data.
ae35377ef5