[FLINK-15454][cluster] Remove redundant inherited ClusterEntrypoint#installSecurityContext

[tisonkun]

What is the purpose of the change

Implementations of ClusterEntrypoint#installSecurityContext is now unique, so that we can remove some dead/duplicated codes.

Brief change log

• Unify overrides of ClusterEntrypoint#installSecurityContext
• Remove unused YarnEntrypointUtils#installSecurityContext

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): (no)
• The serializers: (no)
• The runtime per-record code paths (performance sensitive): (no)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (yes, only code refactor)
• 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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Automated Checks

Last check on commit 44abb7e (Thu Jan 02 08:53:13 UTC 2020)

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CI report:

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• 258c692 Travis: SUCCESS Azure: SUCCESS
• a8fbdec Travis: SUCCESS Azure: SUCCESS

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[tisonkun]

bisec change 8101c0d

[aljoscha]

Nicely spotted! 🍵