revert: implement Serializable for ThresholdedRandomCutForestState

[ylwu-amzn]

Signed-off-by: Yaliang Wu ylwu@amazon.com

AD is using protostuff to serialize/deserialize RCF model. With the change "implement Serializable for ThresholdedRandomCutForestState", AD can't deserialize old models. So we have to revert this change. At the same time, we will use the same way of AD to serialize/deserialize RCF in ml-commons.

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[ylwu-amzn]

Tested every commit after PR #282 (AD is using this commit in 1.3.0), after PR #284 , RCF code can't deserialize 1.3.0 AD RCF model any more. This is different with yesterday's test result that RCF commit 2fedfea can deserialize AD 1.3.0 model. Will confirm with @amitgalitz to learn why the test results are different.
But we still prefer to revert the PR #282 to not add any overhead about AD BWC. And we plan to use the same way of AD to serialize/deserialize RCF model. That will make our future BWC support easier. But cons is we have 2 serialization ways in ml-commons. Check PR opensearch-project/ml-commons#251

Check more details on this issue #305 (comment)

To test the impact of my PR #298 , I applied it to commit 3bb8fce (PR #283) which used by AD 1.3.0, check my branch https://github.com/ylwu-amzn/random-cut-forest-by-aws/tree/test_ad_protostuff, commit ylwu-amzn@bc7944e. Test locally, it can parse AD 1.3.0 model successfully.

[ylwu-amzn]

As explained above, PR #298 doesn't impact the deserialization of old AD model. And Sudipto fixed the backward compatibility issue in PR #309. So seems no need to revert the PR #298. Will close this PR for now. If we find PR #298 impacts any part, will revert then.