[8.5] [DOCS] Removes frozen indices limitation item from anomaly detection docs (backport #2828)

[mergify]

Overview

This PR removes a anomaly detection limitation item about frozen indices that no longer applies from docs.

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This is an automatic backport of pull request #2828 done by Mergify.

[mergify]

Cherry-pick of 04632d2 has failed:

On branch mergify/bp/8.5/pr-2828
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Unmerged paths:
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	both modified:   docs/en/stack/ml/anomaly-detection/ml-limitations.asciidoc

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