mkfs-util: Drop batch (b) and n flags from mcopy

mkfs-util: Drop batch (b) and n flags from mcopy

The batch flag is bugged on older versions of mcopy causing failures
such as:

```
Internal error, size too big
Streamcache allocation problem:: 5
```

It's also a little unclear what the batch flag actually does, so since
everything still works without it, it doesn't hurt to remove it.

The n flag only applies when copying from fat to unix which we don't do
so it doesn't make sense in this scenario.