Docs(Enterprise): Notify that offline restore feature is deprecated

[kevinmingtarja]

Description:

The offline restore feature is deprecated (v21.03.0 was the last version to have it), but it is not stated in the docs, which might confuse readers. So, I think we should do something to notify of this change.

[skrdgraph]

@kevinmingtarja it would be good to point to the dgraph code / commit where this was deprecated.

@MichelDiz this is exactly the reason why docs & code should go together

[kevinmingtarja]

@skrdgraph Actually after further digging, I found these two slack threads, and from these two it seems like they only deprecated it in a separate release branch for cloud release/v21.03-slash (https://github.com/dgraph-io/dgraph/commits/release/v21.03-slash). I'm still trying to find the exact commit where the change happened. It's also possible that they did not end up bringing the changes from this cloud branch to the actual v21.03. I'll let you know if I find anything.

https://dgraphlabs.slack.com/archives/C019WF554MB/p1619198987277300

https://dgraphlabs.slack.com/archives/CSH96QK62/p1621279945315600?thread_ts=1621278898.313900&cid=CSH96QK62

[skrdgraph]

@kevinmingtarja we will skip it for the current doc release, and we can always add this in next week as a fix to our released docs.