[DOC] Remove Segment Replication warning on alerting compatibility.

[mch2]

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With #4967 we added a warning that alerting was not compatible with segment replication. This has since been resolved with opensearch-project/alerting#1205 and this warning can be removed. This is item 3 in https://opensearch.org/docs/latest/tuning-your-cluster/availability-and-recovery/segment-replication/index/#considerations.

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