[FLINK-37101] Remove legacy internal methods for changing serializer behavior in SerializerConfig

[X-czh]

What is the purpose of the change

There're a few @internal "set" methods in the SerializerConfig interface that can change serializer behavior, which remained there waiting for all their deprecated caller methods to be removed. Now that the caller methods are removed in Flink 2.0, we should remove these "set" methods now.

Brief change log

Remove legacy internal methods for changing serializer behavior in SerializerConfig.

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

Not applicable.

[flinkbot]

CI report:

• 2fcc6fc Azure: SUCCESS

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