postrm is in ubuntu-sugar-remix-default-settings 0.5.
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  | #!/bin/sh
set -e
case "$1" in
  remove|purge)
    if which update-gconf-defaults >/dev/null 2>&1 && [ -d /usr/share/gconf/mandatory/usr ]; then
        update-gconf-defaults --source /usr/share/gconf/usr/mandatory \
        --destination /var/lib/gconf/usr.mandatory
        update-gconf-defaults --source /usr/share/gconf/usr/default \
        --destination /var/lib/gconf/usr.default
    fi
    if [ -d /var/lib/gconf/usr.mandatory ]; then
        rm -rf /var/lib/gconf/usr.mandatory
    fi
    if [ -d /var/lib/gconf/usr.mandatory ]; then
        rm -rf /var/lib/gconf/usr.default
    fi
    if [ -x /usr/lib/gdm/gdm-set-default-session ] ; then
        /usr/lib/gdm/gdm-set-default-session --remove usr || true
    fi
    ;;
esac
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