ipfs files ls documentation error - only works with MFS

### Checklist

- [X] I am reporting a documentation issue in this repo, not https://docs.ipfs.tech.
- [X] I have searched on the [issue tracker](https://github.com/ipfs/kubo/issues?q=is%3Aissue) for my issue.

### Location

https://github.com/ipfs/kubo/blob/255e64e49e837afce534555f3451e2cffe9f0dcb/core/commands/files.go#L451

### Description

This PR seems to have introduced erroneous documentation https://github.com/ipfs/kubo/pull/7755. `ipfs files ls /ipfs/` errors.

Solutions are to either revert that line and make it clear it only does MFS (unlike `ipfs files stat`) and direct people to `ipfs ls` or add support for `/ipfs` in `ipfs files ls` as we have for `ipfs files stat`. Of course this comes with the same caveat as for `stat` that life is hard for anyone who has decided to use `/ipfs` as a folder in their MFS root.