[Cleanup] Optimize theme typescript build

[sserrata]

Description

Previously, our theme tsc build step used babel to transpile to both esm and cjs. With node 16+ this step is unnecessary. Furthermore, emitting to both lib and lib-next can sometimes lead to unexpected behavior at runtime.

Motivation and Context

From docusaurus maintainer:

Also latest Docusaurus is on Node 16.14 with ESM support, you may not need 2 theme outputs (esm+cjs) now. We removed cjs recently from the classic theme

I mean you don't need to compile the theme in esm + cjs, like we used to
"babel:lib": "cross-env BABEL_ENV=lib babel src -d lib --extensions ".tsx,.ts" --ignore "/.d.ts" --copy-files",
"babel:lib-next": "cross-env BABEL_ENV=lib-next babel src -d lib-next --extensions ".tsx,.ts" --ignore "/.d.ts" --copy-files",

How Has This Been Tested?

Tested locally. Deploy preview will test prod deployment. Further testing will be needed using standalone docusaurus site.

[github-actions]

Visit the preview URL for this PR (updated for commit aa4e048):

https://docusaurus-openapi-36b86--pr524-g8cq301q.web.app

_{(expires Sun, 23 Apr 2023 17:11:05 GMT)}

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