bug#57503: 28.1.91; package-selected-packages should not be saved to custom-file

[Lars Ingebrigtsen]

Robert Pluim <rpluim@gmail.com> writes:

> Iʼm not convinced thatʼs necessary. I just did the following:
>
> 1. emacs-29+my patch, install some packages => no package-selected-packages
> setting
> 2. emacs-28, run `package-list-packagesʼ => package-selected-packages
> is populated with packages set in step 1, and saved in .emacs

Oh, I didn't know that it was automatically recreated.  Then what's the
point of the variable?  According to the doc string:

---
Store here packages installed explicitly by user.
---

Does 2) there get that right, or does it contain all packages installed,
explicitly or not?