Dear Maintainer,
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.

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

$ pkg=xserver-xorg-video-radeon ; adequate $pkg ; dpkg-query -W
-f='${Conffiles}\n' $pkg | grep obsolete
xserver-xorg-video-radeon: obsolete-conffile /etc/modprobe.d/radeon-kms.conf
 /etc/modprobe.d/radeon-kms.conf 3792130931629c4398df31ffa5dd0d9c obsolete

The bug is modelled on Paul Wise's bug #726082 .

Please lemme know if any more info. is needed. This is on relatively a
newish install (only couple of months old.)

Please note Debian Policy version 3.9.5.0 at section:

10.7.3
          Packages should remove all obsolete configuration files without
          local changes during upgrades.  The `dpkg-maintscript-helper'
          tool, available from the `dpkg' package since _Wheezy_, can help
          with this.

Cheers!
Martin-Éric