create-index: remove the description that no stats are collected for mv index

[time-and-fate]

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

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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 (in Chinese).

• master (the latest development version)
• v7.6 (TiDB 7.6 versions)
• v7.5 (TiDB 7.5 versions)
• v7.4 (TiDB 7.4 versions)
• v7.3 (TiDB 7.3 versions)
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• v6.5 (TiDB 6.5 versions)
• v6.1 (TiDB 6.1 versions)
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• v5.3 (TiDB 5.3 versions)
• v5.2 (TiDB 5.2 versions)
• v5.1 (TiDB 5.1 versions)
• v5.0 (TiDB 5.0 versions)

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

• This PR is translated from:
• Other reference link(s): Support cost-based access path selection for the multi-valued index tidb#46539

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]

[LGTM Timeline notifier]

Timeline:

• 2024-01-02 03:04:52.234124878 +0000 UTC m=+2139783.271351789: ☑️ agreed by ran-huang.
• 2024-01-02 04:05:34.743037117 +0000 UTC m=+2143425.780264045: ☑️ agreed by hfxsd.

[ran-huang]

/approve

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ran-huang

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