br: remove an unclear usage tip about checksum

[shichun-0415]

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[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• ran-huang

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[shichun-0415]

/verify

[IANTHEREAL]

LGTM

[shichun-0415]

/status LGT1

[shichun-0415]

/merge

[ti-chi-bot]

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

Commit hash: 0dc4cd1

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #10538.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #10539.