[FLINK-35227][rest] Remove execution-mode in ExecutionConfigInfo

[1996fanrui]

What is the purpose of the change

[FLINK-35227][rest] Remove execution-mode in ExecutionConfigInfo

Brief change log

[FLINK-35227][rest] Remove execution-mode in ExecutionConfigInfo

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): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): yes
• 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:

• 3f535f1 Azure: SUCCESS

Bot commands

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

[1996fanrui]

Hi @RocMarshal , would you mind reviewing this PR in your free time? thanks~

[RocMarshal]

Thanks @1996fanrui for the contribution.
LGTM +1. 👍