Removed Platform.web (#23830)

Summary:
Initially if a `react-native-web` project were to use a library that required internals `expo/webpack-config` would polyfill those internals. This `Platform.web` was used for cases where `react-native` modules needed other internal `react-native` modules, ex: `Animated/src/AnimatedEvent -> Renderer/shims/ReactNative -> Renderer/oss/ReactNativeRenderer-dev -> Core/InitializeCore -> Devtools/setupDevtools -> WebSocket/WebSocket -> Utilities/Platform`

The consensus is that if any `react-native` library references a `react-native` internal (ex: `react-native/*`), it should continue to throw errors. We've removed the use of internals from all of the Unimodules, `react-navigation`, and `react-native-gesture-handler`. This covers a wide enough area for a lot of projects to get web support.

* Add emitters for libs referencing internals necolas/react-native-web#1275
* Remove monkey patch that bundles RN, libs that use internals will crash instead expo/expo-cli#409
* Remove all unsupported internals and polyfills from the Expo suite expo/expo#3676
* Remove internals from react-native-gesture-handler kmagiera/react-native-gesture-handler#406

* Related #23387

[GENERAL] [REMOVED] - Platform.web.js
Pull Request resolved: https://github.com/facebook/react-native/pull/23830

Differential Revision: D14406145

Pulled By: hramos

fbshipit-source-id: bdda99a334d33f5543fdb954eb80e2e7186f985a

Libraries/Utilities/Platform.web.js

@@ -1,24 +0,0 @@
-/**
- * Copyright (c) 2015-present, Facebook, Inc.
- *
- * This source code is licensed under the MIT license found in the
- * LICENSE file in the root directory of this source tree.
- *
- * @format
- * @flow
- */
-
-'use strict';
-
-export type PlatformSelectSpec<D, I> = {
-  default?: D,
-  web?: I,
-};
-
-const Platform = {
-  OS: 'web',
-  select: <D, I>(spec: PlatformSelectSpec<D, I>): D | I =>
-    'web' in spec ? spec.web : spec.default,
-};
-
-module.exports = Platform;