cdc: remove 2.4.0 as the default kafka version keyword

[3AceShowHand]

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[3AceShowHand]

/hold

[3AceShowHand]

After support kafka automatical detection, just remove kafka-verison keyword from the sink-uri example, to make it less confusing.

[qiancai]

Removed the needs-cherry-pick-release-7.6 label because the v7.6 docs have been archived at https://docs-archive.pingcap.com/zh/tidb/v7.6 and will no longer receive new updates.

[qiancai]

Removed the needs-cherry-pick-release-8.0 label because the v8.0 docs have been archived at https://docs-archive.pingcap.com/zh/tidb/v8.0 and will no longer receive new updates.

[qiancai]

Removed the needs-cherry-pick-release-8.2 label because the v8.2 docs have been archived at https://docs-archive.pingcap.com/zh/tidb/v8.2 and will no longer receive new updates.