pd: remove shuffle schedulers

[rleungx]

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What is changed, added or deleted? (Required)

These schedulers are mainly used in testing and they should not be exposed to the users.

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• master (the latest development version)
• v8.3 (TiDB 8.3 versions)
• v8.2 (TiDB 8.2 versions)
• v8.1 (TiDB 8.1 versions)
• v8.0 (TiDB 8.0 versions)
• v7.5 (TiDB 7.5 versions)
• v7.1 (TiDB 7.1 versions)
• v6.5 (TiDB 6.5 versions)
• v6.1 (TiDB 6.1 versions)
• v5.4 (TiDB 5.4 versions)
• v5.3 (TiDB 5.3 versions)
• v5.2 (TiDB 5.2 versions)

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• Delete files
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[qiancai]

/approve

[qiancai]

/approve

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.1: #18559.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.2: #18563.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.3: #18564.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-5.3: #18565.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-5.4: #18566.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #18567.