master/5.0: remove low-version descriptions

[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)

Removed the descriptions about the lower product versions according to the conclusion made in #4549

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: master/5.0: remove low-version descriptions docs-cn#5775
• 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

[Joyinqin]

/label needs-cherry-pick-5.0
/translation from-docs-cn

[Joyinqin]

/label v5.0

[TomShawn]

LGTM

[ti-chi-bot]

[REVIEW NOTIFICATION]

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• TomShawn

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[TomShawn]

/label require-LGT1

[TomShawn]

/merge

[ti-chi-bot]

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

Commit hash: bec7c72

[ti-srebot]

cherry pick to release-5.0 in PR #5539