[FLINK-37691] Do not remove ChangelogNormalize if deduplication was requested

[dawidwys]

What is the purpose of the change

Do not try removing ChangelogNormalize if "table.exec.source.cdc-events-duplicate" = "true"

Verifying this change

Added a plan test

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

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

[flinkbot]

CI report:

• 09701fe Azure: CANCELED
• 4e86769 Azure: PENDING

Bot commands

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• @flinkbot run azure re-run the last Azure build

[twalthr]

One minor nit. Otherwise LGTM.