postrm is in apt-transport-spacewalk 1.0.6-2.1.
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 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34  | #! /bin/sh
set -e
hook=/etc/apt/apt.conf.d/50spacewalk
case "$1" in
    purge)
        rm -f $hook.disabled
        ;;
    remove)
        mv $hook $hook.disabled
        ;;
    abort-install)
        if test "x$2" != "x" && test -f $hook
        then
            mv $hook $hook.disabled
        fi
        ;;
    upgrade|failed-upgrade|abort-upgrade|disappear)
        ;;
    *)
        echo "postrm called with unknown argument \`$1'" >&2
        exit 1
esac
exit 0
 |