[task][hotfix] Remove PipelinedSubpartition.addBufferConsumer method

[rkhachatryan]

What is the purpose of the change

Remove duplicated PipelinedSubpartition.addBufferConsumer method and use PipelinedSubpartition.add() instead.

Verifying this change

This change is a trivial rework 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, Kubernetes/Yarn/Mesos, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? no

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Automated Checks

Last check on commit 04f8d71 (Wed Oct 14 21:19:06 UTC 2020)

Warnings:

• No documentation files were touched! Remember to keep the Flink docs up to date!

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Review Progress

• ❓ 1. The [description] looks good.
• ❓ 2. There is [consensus] that the contribution should go into to Flink.
• ❓ 3. Needs [attention] from.
• ❓ 4. The change fits into the overall [architecture].
• ❓ 5. Overall code [quality] is good.

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[flinkbot]

CI report:

• 0a808e9 Azure: FAILURE

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[rkhachatryan]

@flinkbot run azure

[rkhachatryan]

CI failure unrelated (FLINK-19469).