How to use remove-on-upgrade to remove a configuration file?

[Ludovic Rousseau <ludovic.rousseau@free.fr>]

Hello,

I am fixing Debian bug #990154.

After some work I am able to remove the obsolete conf file using:
rm_conffile /etc/reader.conf.d/0comments 1.9.3-2~ pcscd
in debian/pcscd.maintscript

Nice.
Now I would like to use the method documented in deb-conffiles
https://manpages.debian.org/unstable/dpkg-dev/deb-conffiles.5.en.html

I would need to add in the DEBIAN/conffiles of the pcscd package the line:
remove-on-upgrade /etc/reader.conf.d/0comments

But how do I generate a .deb package with this extra line?
What is the magic dh command or file to do that?
Where is it documented?

I tried to use a file debian/pcscd.conffiles but this file is no more used with debhelper version 12
https://manpages.debian.org/buster/debhelper/dh_installdeb.1.en.html

I searched for occurrences of "remove-on-upgrade" in https://codesearch.debian.net/ but I only find references to dpkg source code.
No Debian package is using or has used "remove-on-upgrade"?

Thanks

--
Dr. Ludovic Rousseau