fix: remove deprecated config.server.base

[fi3ework]

Description

I randomly found server.base (https://vitejs.dev/config/server-options.html#server-base), but it seems like it is not being used anymore. The code was introduced in this pull request (before vite2 was released), but it appears to have not been invoked after a long period of code iteration. The documentation was introduced in this pull request. I suppose the root base config has superseded server.base now.

Additional context

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[bluwy]

Never noticed there's this option before. Looks like a good change to me and doesn't seem to break things.

[sapphi-red]

I read the changes of #7289. It seems the PR added server.base to the types and the docs, but the PR didn't use that anywhere.