[FLINK-22952][azure] Remove Ruby usage

[zentol]

Since the docs have been migrated to hugo we no longer need ruby.

This PR is applicable to master and release-1.13.

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Last check on commit 27e3f24 (Sat Aug 28 12:15:33 UTC 2021)

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• 27e3f24 Azure: FAILURE

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[rmetzger]

Thanks for fixing this!