chore: simplify rollup.config.mjs

[swiing]

Since #6425, the package only exports ESM modules. As a consequence, the rollup configuration does not need to export an array of configuration objects, and as yet another consequence, there is no need to define a base config that could be shared.

Changed

Refactor rollup configuration to export a simple default object directly instead of an array.

Rollout strategy

• Patch release
• Minor release
• Major release; if selected, include a written rollout or migration plan
• None; if selected, include a brief description as to why

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Storybook)
• Changes are SSR compatible
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge
• (GitHub staff only) Integration tests pass at github/github (Learn more about how to run integration tests)

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Latest commit: 9f403f1

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[jonrohan]

Thanks for the PR, we have another one coming that will cover this though #7300