feat(storage): remove shared buffer compaction grouped payload

[Li0k]

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What's changed and what's your intention?

After #18053, hummock can split CN submitted ssts based on table stats, so there is no longer the problem of multiple compaction groups being interfered with due to inaccurate sizes.

So we can remove the logic of submitting ssts by compaction group on the CN side to reduce logic complexity and upload iops. This isn't a radical optimization , but I think it simplifies the logic on the CN side and is worth making as a separate change.

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[Li0k]

test with multi group

https://buildkite.com/risingwave-test/nexmark-benchmark/builds/4430

[hzxa21]

LGTM

[wenym1]

LGTM!

[Li0k]

#15973