The recent upgrade did not deal with obsolete conffiles properly.
Please use the dpkg-maintscript-helper support provided by
dh_installdeb to remove these obsolete conffiles on upgrade.

https://www.debian.org/doc/debian-policy/ch-files.html#s-config-files
https://manpages.debian.org/man/1/dh_installdeb

This bug report brought to you by adequate:

https://bonedaddy.net/pabs3/log/2013/02/23/inadequate-software/

   $ p=gnome-software ; adequate $p ; dpkg-query -W -f='${Conffiles}\n' $p | grep obsolete
   gnome-software: obsolete-conffile /etc/xdg/autostart/gnome-software-service.desktop
    /etc/xdg/autostart/gnome-software-service.desktop e9aa76e7f13a9dc704e2da2bc785c053 obsolete