bug#44366: 26.2: package-delete not removing all obsolete versions of a package

[Boruch Baum]

emacs-version: 26.2 (debian)

  NOTE: This is a follow-up to bug report #44306.

When several versions of a package accumulate (in my case, it seems to
have arisen because operations of `package-autoremove' failed in
mid-course), then package-autoremove only deletes the single most recent
obsolete version of the package. For example, in examining my *Messages*
buffer, I see that one run of the function reported

   Package `popup-20200610.317' deleted.

A next run of the function reported

   Package `popup-20200531.742' deleted.

Finally, the most recent run of the function reported:

   Package `popup-0.5.8' is a system package, not deleting

My expectation is that all obsolete versions of a package should be
removed on the first run of the function.

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