fix: remove references to corepack

[bolinfest]

Currently, our npm publish logic is failing.

There were a number of things that were merged recently that seemed to contribute to this situation, though I think we have fixed most of them, but this one stands out:

#10115

As best I can tell, we tried to fix the pnpm version to a specific hash, but we did not do it consistently (though shell-tool-mcp/package.json had it specified twice...), so for this PR, I ran:

$ git ls-files | grep package.json
codex-cli/package.json
codex-rs/responses-api-proxy/npm/package.json
package.json
sdk/typescript/package.json
shell-tool-mcp/package.json

and ensured that all of them now have this line:

  "packageManager": "pnpm@10.28.2+sha512.41872f037ad22f7348e3b1debbaf7e867cfd448f2726d9cf74c08f19507c31d2c8e7a11525b983febc2df640b5438dee6023ebb1f84ed43cc2d654d2bc326264"

I also went and deleted all of the corepack stuff that was added by #10115.

If someone can explain why we need it and verify it does not break npm publish, then we can bring it back.