Remove index.js.flow shim from Node packages (#49461)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/49461

Flow now supports Package Exports 🎉. This means we can delete the compatiblity pattern in each of our build-enabled Node.js packages.

This simplifies the internal package structure needed to support Flow while developing from source in the monorepo — no prod impact.

Changelog: [Internal]

Reviewed By: cipolleschi

Differential Revision: D69741143

fbshipit-source-id: 070715cb6beb00eb393186dbf95856ceb87fabef

packages/community-cli-plugin/index.js.flow

@@ -1,12 +0,0 @@
-/**
- * Copyright (c) Meta Platforms, Inc. and affiliates.
- *
- * This source code is licensed under the MIT license found in the
- * LICENSE file in the root directory of this source tree.
- *
- * @flow
- * @format
- * @oncall react_native
- */
-
-export * from './src';

packages/dev-middleware/index.js.flow

@@ -1,12 +0,0 @@
-/**
- * Copyright (c) Meta Platforms, Inc. and affiliates.
- *
- * This source code is licensed under the MIT license found in the
- * LICENSE file in the root directory of this source tree.
- *
- * @flow
- * @format
- * @oncall react_native
- */
-
-export * from './src';

packages/react-native-compatibility-check/index.js.flow

@@ -1,12 +0,0 @@
-/**
- * Copyright (c) Meta Platforms, Inc. and affiliates.
- *
- * This source code is licensed under the MIT license found in the
- * LICENSE file in the root directory of this source tree.
- *
- * @flow
- * @format
- * @oncall react_native
- */
-
-export * from './src';

scripts/build/README.md

@@ -72,13 +72,11 @@ packages/
       index.js       # Entry point wrapper file (calls babel-register.js) (compiled away)
       index.flow.js  # Entry point implementation in Flow
       [other files]
-    index.js.flow    # Shim for the Flow typechecker
     package.json     # Includes "exports" field, ideally only src/index.js
 ```
 
 Notes:
 
-- The additional root `index.js.flow` shim is needed due to Flow itself not supporting Package Exports.
 - To minimize complexity, prefer only a single entry of `{".": "src/index.js"}` in `"exports"` for new packages.
 
 ## Build behavior