The following packages were automatically installed and are no longer required: php7.0-curl php7.0-gd php7.0-xml

That depends on whether you have applications that require those libraries. We can't know that.

They weren't installed as part of the normal Virtualmin install process, AFAIK (though they might be pulled in as automatic dependencies, I'm not sure). They are harmless to have installed, unless you're really low on disk space (though they're also very small).

I'd be more inclined to install them so they don't get auto-removed by accident (apt/dpkg have a really weird and confusing and occasionally dangerous notion about installation and dependencies that I've never liked; the other way to get rid of the message is to run apt-get install php7.0-curl php7.0-gd php7.0-xml so they are no longer installed because of dependencies but because you asked for them). Presumably you've installed something at some point that needed them; if that's no longer true, you could remove them. apt-get also has the autoremove command to remove all "no longer needed" packages.