[FLINK-37661] Remove Kryo serializer reference data from version 1.x

[X-czh]

Flink 2.0 has done a major Kryo 2.x -> 5.x upgrade and the new Flink is not compatible with older Kryo state. Reference data from version 1.x can be safely deleted as a result.

[flinkbot]

CI report:

• d3ac3b03edc7e220ddbed0447e65d2e5b94ec01c Azure: SUCCESS

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[X-czh]

@davidradl The FLIP was abandoned for a while and it was decided later to fully drop Kryo v2 support (and hence compatibility from 1.x series) in https://lists.apache.org/thread/odhglx8tmpdt6jnorgcsvxjqjfd169x6.

[davidradl]

Thanks @X-czh , I see it was agreed to fully drop Kryo v2 support (and hence compatibility from 1.x series). For me it still makes sense to have a migration path, as this will hit many users and potentially be the biggest migration inhibitor. I am willing to implement under your guidance, if this helps - as I feel this is very important.

[X-czh]

@Zakelly Last time I heard that there was plan for a state migration tool. How's that going now? If the tool is available, it might not be a big issue to fully drop Kryo v2 support cc @davidradl

[Zakelly]

@X-czh I'm not working on this and I heard there is no detailed plan for now. It seems that no one is driving that currently.

[X-czh]

@davidradl I've initiated a new FLIP(Dicussion thread: https://lists.apache.org/thread/98hsjdpkcrvb9x2sc9pj9f4lkg0td2dc) to support custom generic type serializer, so that users who used Kryo and wanted to upgrade from 1.x can continue to use the Kryo-v2.24 serializer. Any suggestions are welcomed.