/usr/share/debhelper/autoscripts/postrm-dzinstance is in zope-debhelper 0.3.15.
This file is owned by root:root, with mode 0o644.
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 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52  | PKG=#DZ-PKG#
INSTANCE=#DZ-INSTANCE#
ZVER=#DZ-ZVER#
DATABASE=#DZ-DATABASE#
if [ -e /usr/share/debconf/confmodule ]; then
    . /usr/share/debconf/confmodule
fi
[ -n "$(echo $INSTANCE)" ] || exit 1
if command -v invoke-rc.d >/dev/null 2>&1; then
	INVOKE="invoke-rc.d zope$ZVER"
else
	INVOKE="/etc/init.d/zope$ZVER"
fi
case "$1" in
  failed-upgrade|abort-install|abort-upgrade|disappear)
    ;;
  upgrade)
    ;;
  remove)
    $INVOKE stop "INSTANCE=$INSTANCE" || true
    dzhandle -z $ZVER remove-instance $INSTANCE || true
    if [ "$DATABASE" = "ZEO" ]; then
	$INVOKE stop "ZEOSERVER=$INSTANCE" || true
        dzhandle -z $ZVER remove-zeoinstance $INSTANCE || true
    fi
    ;;
  purge)
    db_get $PKG/keep-data-on-purge 2>/dev/null || true
    if [ "$RET" = yes ]; then
	    echo >&2 "$PKG is configured to keep the data file on purge"
    else
        if [ "$DATABASE" = "ZEO" ]; then
            dzhandle -z $ZVER purge-zeoinstance $INSTANCE || true
        fi
        rm -rf "/var/lib/zope$ZVER/instance/$INSTANCE" \
               "/var/log/zope$ZVER/$INSTANCE" \
               "/etc/zope$ZVER/$INSTANCE"
    fi
    ;;
  *)
    echo "postrm called with unknown argument \`$1'" >&2
    exit 1
esac
 |