[FLINK-12230][runtime] Remove method JobMaster#getExecutionGraph()

[GJL]

What is the purpose of the change

Remove method JobMaster#getExecutionGraph(). This is needed because the JobMaster will not have access to the ExecutionGraph in future

Brief change log

• Remove method JobMaster#getExecutionGraph()

Verifying this change

This change is already covered by existing tests, such as JobMasterTest.

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, Yarn/Mesos, 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)

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Review Progress

• ✅ 1. The [description] looks good.
  • Approved by @tillrohrmann [PMC]
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  • Approved by @tillrohrmann [PMC]
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• ✅ 4. The change fits into the overall [architecture].
  • Approved by @tillrohrmann [PMC]
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  • Approved by @tillrohrmann [PMC]

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[tillrohrmann]

Thanks for providing this fix @GJL. LGTM. +1 for merging.

[tillrohrmann]

@flinkbot approve all

[GJL]

Thanks for the review. I rebased to latest master and will merge as soon as build is green.