Remove old react-fetch, react-fs and react-pg libraries (#25577)

To avoid confusion. We are patching `fetch`, and only `fetch`, for a
small fix scoped to react renders elsewhere, but this code is not it.

This code was for the strategy used in the original [React Server
Components demo](https://github.com/reactjs/server-components-demo).
Which [we
announced](https://reactjs.org/blog/2022/06/15/react-labs-what-we-have-been-working-on-june-2022.html)
that we're moving away from in favor of [First class support for
promises and async/await](https://github.com/reactjs/rfcs/pull/229).

We might explore using these package for other instrumentation in the
future but not now and not like this.