[FLINK-37711] Remove unused getJobGraph from PipelineExecutorUtils

[beliefer]

What is the purpose of the change

This PR aims to remove unused getJobGraph from PipelineExecutorUtils.
The method getJobGraph in PipelineExecutorUtils is only used in test cases.
The client uses StreamGraph now. We should update these test cases.

Brief change log

Remove unused getJobGraph from PipelineExecutorUtils.

Verifying this change

This change is already covered by existing tests, such as (DefaultPackagedProgramRetrieverITCase).

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)

[flinkbot]

CI report:

• cfeea4b Azure: SUCCESS

Bot commands

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[beliefer]

@davidradl Thank you!

[snuyanzin]

can we extract this

streamGraph.getClasspaths().stream()
                        .map(URL::toString)
                        .collect(Collectors.toList());

into a separate method, it is duplicated in this class multiple times

[beliefer]

Done.

[beliefer]

@snuyanzin Thank you!