[depot_autoremove] Removing outdated PGKs from the depot

[Alice Domage]

Dear Norman,

I hope this e-mail finds you well. Please excuse the long delay on that 
matter.

I have proceeded with the implementation following your guidelines. I 
came up with the following solution [1].

We have yet to discuss reporting. At first, it was not a needed feature. 
However, this is very useful for our management component. So I have 
included it with this proposal.

It is handier to proceed with code review on GitHub. I will open an 
issue [1] and mention it on my topic branch.

I hope this is okay with you to move the conversation on GitHub.

[1] https://github.com/genodelabs/genode/issues/4866

Cheers,
Alice