postrm is in fontconfig 2.8.0-3ubuntu9.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10  | #! /bin/sh
set -e
case "$1" in
	purge)
	    rm -f /var/log/fontconfig.log
	    rm -rf /var/cache/fontconfig
	    ;;
esac
 |