Docs: remove solved issues from Package Registry docs

What does this MR do and why?

In #329253 (closed), we implemented a new feature. In the docs, we mentioned some open issues. In the meantime, the following issues are solved:

• Support package registry visibility in the Ruby... (#385259 - closed)
• Support package registry visibility in the Debi... (#385258 - closed)

So let's remove them in the docs.

/cc @10io

🛠 with ❤ at Siemens

/cc @bufferoverflow

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