[FLINK-15308][runtime] Remove data compression for pipelined shuffle.

[wsry]

What is the purpose of the change

This PR removes data compression for pipelined shuffle mode. The feature may be added in the future version of Flink if there is a better solution.

Brief change log

• The code and document relevant to data compression for pipeline mode is removed.

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): (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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Automated Checks

Last check on commit a8a9d94 (Thu Dec 19 10:25:28 UTC 2019)

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CI report:

• c09e6a1 UNKNOWN
• a2c34a0 Travis: SUCCESS Azure: SUCCESS
• 919abd2 Travis: FAILURE Azure: SUCCESS
• 9322dfa Travis: PENDING Azure: SUCCESS

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[zhijiangW]

we should also adjust the method description above.

[zhijiangW]

Thanks for the fix @wsry!
Almost LGTM except for one tiny comment. In addition, can you add some messages in commit for the reason of removing pipelined compression?

[wsry]

Thanks for the review @zhijiangW . I have updated the PR.