ZED/zfs-list-cacher.sh: don't exit on ignored event type

Check for the history_event type instead.

The zfs-list-cacher.sh script currently respects the event types
excluded from syslog(!) in ZED_SYSLOG_SUBCLASS_EXCLUDE.
This makes little sense in this single-purpose script and
silently breaks when history_events are excluded from syslog,
which is the default since 13d65987a9d9958de77422f5d9d25b47e486537d.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: InsanePrawn <insane.prawny@gmail.com>
Closes #11164
Closes #11347