CI: Remove NTP test

[DL6ER]

What does this implement/fix?

This PR removes the NTP test from FTL's CI testing suite. The reason for this is that this test is failing > 75% of the time, triggering automatic retries unnecessarily lengthening the overall build process and wasting resources.

But it is actually not only wasting resources but also causes more than 80% of the docker-base-images/ftl-build to fail at least one of the jobs, preventing updating the build container altogether.

There simply seems to be no reliable way to get this working. The underlying issue is somewhat hard to analyze, however, it seems that the NTP server simply is firewalled away on most (but not all) GHA runners.

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Related issue or feature (if applicable): N/A

Pull request in docs with documentation (if applicable): N/A

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