Bug#987017: recommends 3 different ways to find obsolete packages, pick one

[Antoine Beaupre <anarcat@debian.org>]

Package: release-notes
Severity: minor

The release notes, in sections 4.2.2 and 4.8, actually suggest *three*
*different* ways of finding what are essential orphaned packages:

    aptitude search '~o'
    aptitude search '?narrow(?installed, ?not(?origin(Debian)))'
    apt-forktracer | sort

Then I also know of those:

    apt-show-versions | grep -v /bullseye
    aptitude search '?narrow(?installed, ?not(?origin(Debian)))'
    aptitude search '?narrow(?not(?archive("^[^n][^o][^w].*$")),?version(CURRENT))'

I frankly don't quite know where I stand with all this anymore, but I
am getting the strong feeling we're sending an incoherent message
here. :)

In my personal documentation, I've settled on `apt-forktracer`, but I
suspect we might want to stick with `aptitude search '~obsolete'`
because that matches other documentation in the release notes (and
allows for easy purging).

Is there any reason why we have all that diversity?

What's the right way to do what we actually want here?

-- System Information:
Debian Release: 10.9
  APT prefers stable-debug
  APT policy: (500, 'stable-debug'), (500, 'stable'), (1, 'experimental'), (1, 'unstable'), (1, 'testing')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.19.0-16-amd64 (SMP w/4 CPU cores)
Locale: LANG=fr_CA.UTF-8, LC_CTYPE=fr_CA.UTF-8 (charmap=UTF-8), LANGUAGE=fr_CA.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled