update tiflash-command-line-flags.md

[hehechen]

What is changed, added or deleted? (Required)

Update tiflash-command-line-flags.md.
dttool migrate no need to stop TiFlash node after pingcap/tiflash#5271 merged.

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• master (the latest development version)
• v6.2 (TiDB 6.2 versions)
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• v5.4 (TiDB 5.4 versions)
• v5.3 (TiDB 5.3 versions)
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• v5.1 (TiDB 5.1 versions)
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• Delete files
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[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• shichun-0415

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[JaySon-Huang]

LGTM

[TomShawn]

@hehechen 是否为 v6.2 特性呢？

[shichun-0415]

LGTM

[shichun-0415]

/remove status LGT1
/status LGT2

[shichun-0415]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 609d77b