postrm is in bve-train-br-class-323-3dcab 20100711-0ubuntu2.
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
    remove|purge)
        dpkg-divert \
	    --package bve-train-br-class-323-3dcab \
	    --rename \
	    --remove /usr/share/games/bve/Train/BR_Class_323/train.dat || true
	;;
esac
 |