logstash: Replace deprecated checksum filter

The checksum filter is being used in our config in an attempt to add
a correlation key to all fatal and exception-json messages. It however
doesn't produce the same checksum. This is a known upstream bug that has
been closed as "REJECTED" with a recommendation to use the anonymize
filter instead.

Change-Id: I5ac97a4090ca81ef0d244ac4e6c7f1fb96c8be35