Remove calls to 6.x ES _xpack/* API endpoints

[ycombinator]

⚠️ DO NOT BACKPORT - should go out only in 8.0.0! ⚠️

What does this PR do?

Removes conditional code that supported Beats talking to various _xpack/* Elasticsearch API endpoints deprecated in 6.x and removed in 7.0 of Elasticsearch.

Why is it important?

Several _xpack/* API endpoints were deprecated in Elasticsearch in 6.x and removed in 7.0. The Beats codebase through 7.x had conditional code to call these endpoints if the Beat was talking to a 6.x Elasticsearch cluster. Starting 8.0.0, Beats should not be expected to talk to a 6.x Elasticsearch cluster, so we can remove these conditional bits of code.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc. Not a user- or developer-facing change.

Related issues

• Relates to Elasticsearch _xpack endpoint is getting deprecated #9424

[elasticmachine]

Pinging @elastic/integrations-services (Team:Services)

[elasticmachine]

💚 Build Succeeded

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Build stats

• Build Cause: [Pull request Remove calls to 6.x ES _xpack/* API endpoints #18609 opened]

• Start Time: 2020-05-18T09:21:11.234+0000

• Duration: 76 min 36 sec (4536269)

Test stats 🧪

Test	Results
Failed	0
Passed	9211
Skipped	1542
Total	10753

Steps errors

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• Name: Install Go 1.13.10

  • Description: .ci/scripts/install-go.sh

  • Result: FAILURE

  • Duration: 1 min 33 sec

  • Start Time: 2020-05-18T09:44:04.980+0000

  • log

• Name: Report to Codecov

  • Description: curl -sSLo codecov https://codecov.io/bash for i in auditbeat filebeat heartbeat libbeat metricbeat packetbeat winlogbeat journalbeat do FILE="${i}/build/coverage/full.cov" if [ -f "${FILE}" ]; then bash codecov -f "${FILE}" fi done

  • Result: FAILURE

  • Duration: 2 min 22 sec

  • Start Time: 2020-05-18T10:14:06.616+0000

  • log

• Name: Install Go 1.13.10

  • Description: .ci/scripts/install-go.sh

  • Result: FAILURE

  • Duration: 1 min 33 sec

  • Start Time: 2020-05-18T09:44:05.518+0000

  • log

• Name: Install docker-compose 1.21.0

  • Description: .ci/scripts/install-docker-compose.sh

  • Result: FAILURE

  • Duration: 1 min 33 sec

  • Start Time: 2020-05-18T09:44:16.818+0000

  • log

• Name: Report to Codecov

  • Description: curl -sSLo codecov https://codecov.io/bash for i in auditbeat filebeat heartbeat libbeat metricbeat packetbeat winlogbeat journalbeat do FILE="${i}/build/coverage/full.cov" if [ -f "${FILE}" ]; then bash codecov -f "${FILE}" fi done

  • Result: FAILURE

  • Duration: 1 min 28 sec

  • Start Time: 2020-05-18T10:20:14.423+0000

  • log