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](reactjs/rfcs#229).

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

.eslintrc.js

@@ -140,8 +140,6 @@ module.exports = {
         'packages/react-dom/src/test-utils/**/*.js',
         'packages/react-devtools-shared/**/*.js',
         'packages/react-noop-renderer/**/*.js',
-        'packages/react-pg/**/*.js',
-        'packages/react-fs/**/*.js',
         'packages/react-refresh/**/*.js',
         'packages/react-server-dom-webpack/**/*.js',
         'packages/react-test-renderer/**/*.js',

ReactVersions.js

@@ -43,7 +43,7 @@ const stablePackages = {
 // These packages do not exist in the @next or @latest channel, only
 // @experimental. We don't use semver, just the commit sha, so this is just a
 // list of package names instead of a map.
-const experimentalPackages = ['react-fetch', 'react-fs', 'react-pg'];
+const experimentalPackages = [];
 
 module.exports = {
   ReactVersion,