Update outdated https://en.pingcap.com/ links (#18096)

[ti-chi-bot]

This is an automated cherry-pick of #18096

What is changed, added or deleted? (Required)

Note: Another option would be to make en.pingcap.com a cname for www.pingcap.com in the DNS settings. I'm not sure which option is best.

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• Delete files
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• Need modification after applied to another branch
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[lilin90]

/approve

[ti-chi-bot]

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