Remove non available stack release versions from integration CI tests

[alexcams]

Plugin CI is broken as we can see in this PR. The reason is that the plugin CI file includes an stack release version that is not available (8.next). This is referenced at: https://github.com/logstash-plugins/.ci/blob/1.x/logstash-versions.yml.

This commit removes unavailable release from integration tests jobs definition to fix the CI.

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[mashhurs]

Do we really need?

[alexcams]

Unless we want to remove tests using manticore, yes we need it. Looks like that dependency was removed from any of the previous requires.

[donoghuc]

Do you have a link to a failed run where you saw this? It looks to me like this is currently running fine https://app.travis-ci.com/github/logstash-plugins/logstash-input-elasticsearch/jobs/635313527

[mashhurs]

@donoghuc the link you have posted is belong to input-elasticsearch, this is filter-elasticsearch but input-es is also with the same case.
I have seen this issue in the past -https://app.travis-ci.com/github/logstash-plugins/logstash-filter-elasticsearch/jobs/635410594
And it looks like transient. I have retried it.

[mashhurs]

And it is 🟢

[mashhurs]

LGTM with a minor suggestion that the failure is actually transient.