postrm is in zabbix-java-gateway 1:2.4.7+dfsg-2ubuntu2.
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 35 36 37 38 39 40  | #!/bin/sh
set -e
case "$1" in
    purge)
        rm -f  /etc/zabbix/zabbix_java_gateway.conf \
               /etc/zabbix/logback-console.xml      \
               /etc/zabbix/logback.xml
        rm -fr /var/log/zabbix-java-gateway
        rm -f  /var/run/zabbix/zabbix_gateway_java.pid
    ;;
esac
# Automatically added by dh_installinit
if [ "$1" = "purge" ] ; then
	update-rc.d zabbix-java-gateway remove >/dev/null
fi
# In case this system is running systemd, we make systemd reload the unit files
# to pick up changes.
if [ -d /run/systemd/system ] ; then
	systemctl --system daemon-reload >/dev/null || true
fi
# End automatically added section
# Automatically added by dh_systemd_enable
if [ "$1" = "remove" ]; then
	if [ -x "/usr/bin/deb-systemd-helper" ]; then
		deb-systemd-helper mask zabbix-java-gateway.service >/dev/null
	fi
fi
if [ "$1" = "purge" ]; then
	if [ -x "/usr/bin/deb-systemd-helper" ]; then
		deb-systemd-helper purge zabbix-java-gateway.service >/dev/null
		deb-systemd-helper unmask zabbix-java-gateway.service >/dev/null
	fi
fi
# End automatically added section
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