`oras logout` not working for non-default auth config

When running `oras logout <registry> --registry-config <path>`, the credential will be removed from default config path (`$home/.docker/config.json`) but not `<path>`.


# Reproduce
```shell
oras login <registry> --registry-config my-config.json
oras logout <registry> --registry-config my-config.json # this command should remove cred in my-config.json but failed to
```