com.sun is an identifier, nothing more. No tooling sees com.sun and assumes, "oh that means I can make an HTTP request to the IP address which sun.com resolves to".

In Go, the package identifiers are literally URLs. Go's own tooling assumes that it can make an HTTP request to the URL and that the response will be HTML with particular tags which Go's tooling will parse and use to resolve a git repository which can be 'git clone'd. Leaving them as-is when you abandon the infrastructure they reference literally means leaving dead links in your source code.