ja: remove files deleted in release-7.5 branch

[Oreoxmt]

What is changed, added or deleted? (Required)

• tidb-cloud/changefeed-replication.md is removed in cloud: remove changefeed replication docs #15567
• tidb-cloud/v7.1.0-performance-benchmarking-with-sysbench.md and tidb-cloud/v7.1.0-performance-benchmarking-with-tpcc.md are removed in cloud: update benchmark results #16918

cd docs-staging/markdown-pages
diff -rq ja/tidbcloud/master en/tidbcloud/master | grep "Only in ja/tidbcloud"
Only in ja/tidbcloud/master/tidb-cloud: changefeed-replication.md
Only in ja/tidbcloud/master/tidb-cloud: v7.1.0-performance-benchmarking-with-sysbench.md
Only in ja/tidbcloud/master/tidb-cloud: v7.1.0-performance-benchmarking-with-tpcc.md

Which TiDB version(s) do your changes apply to? (Required)

Tips for choosing the affected version(s):

By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.

For details, see tips for choosing the affected versions.

• 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)

What is the related PR or file link(s)?

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• Other reference link(s):

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[lilin90]

/lgtm

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-08-14 03:15:40.01462796 +0000 UTC m=+324224.718097595: ☑️ agreed by lilin90.