[FLINK-39702] Exclude netty 3.x from hadoop

[snuyanzin]

What is the purpose of the change

Netty 3 still comes with hadop, however at the same time (could be checked with ./mvnw dependency:tree ) there is also netty4. Thus Netty3 becomes useless and all the tests pass without it
Probably it makes sense to exclude it then

Brief change log

pom

Verifying this change

existing tests

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

• Dependencies (does it add or upgrade a dependency): ( no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (no)
• The serializers: (no)
• The runtime per-record code paths (performance sensitive): (no )
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (no)
• The S3 file system connector: (no)

Documentation

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

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• 308c902 Azure: SUCCESS

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[snuyanzin]

@mateczagany may be you can take a look here as you made some work with netty upgrade

[mateczagany]

I agree, makes sense to get rid of Netty 3.x here. I found no issues with this locally