sql-statements: delete the file that does not apply for v4.0

[Joyinqin]

First-time contributors' checklist

• I've signed Contributor License Agreement that's required for repo owners to accept my contribution.

What is changed, added or deleted? (Required)

Delete the file that does not apply for v4.0.

• sql-statements/sql-statement-alter-index.md

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

• master (the latest development version)
• v5.0 (TiDB 5.0 versions)
• v4.0 (TiDB 4.0 versions)
• v3.1 (TiDB 3.1 versions)
• v3.0 (TiDB 3.0 versions)
• v2.1 (TiDB 2.1 versions)

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

• This PR is translated from:
• Other reference link(s): sql-statements: use EBNF to render syntax diagrams for ADD, ALTER and ANALYZE statements #4722

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

[Joyinqin]

/cc CharLotteiu

[Joyinqin]

/cc ran-huang

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• CharLotteiu

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

The full list of commands accepted by this bot can be found here.

Reviewer can indicate their review by writing /lgtm in a comment.
Reviewer can cancel approval by writing /lgtm cancel in a comment.

[Joyinqin]

/translation from-docs-cn

[ran-huang]

/lgtm

[ti-chi-bot]

@Joyinqin: you cannot /lgtm your own PR.

In response to this:

/lgtm

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[Joyinqin]

/cc @TomShawn

[ran-huang]

You only need 1 LGTM for PR based on release-4.0, so bot won't read my LGTM

[TomShawn]

@Joyinqin Could you provide the docs-cn PR from which this PR is translated?

[ti-chi-bot]

@Joyinqin: These labels are not set on the issue: translation/from, translation/docs, translation/cn.

In response to this:

/remove-translation from docs cn

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[ti-chi-bot]

@Joyinqin: These labels are not set on the issue: translation/from, translation/docs, translation/cn.

In response to this:

/remove-translation from docs cn

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[Joyinqin]

/translation no-need

[TomShawn]

/remove-translation from-docs-cn

[TomShawn]

/merge

[ti-chi-bot]

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

Commit hash: 401ba1b