BREAKING - Remove React forwarding and wrong import warnings

Summary:
Importing `react` modules from `react-native` has been deprecated since 0.25 so I think it's safe to remove it now since everyone has migrated their code and it is now well know and documented that you import from different packages. This finishes the spring cleanup of `react-native-implementation.js` :)

**Test plan**
Tested that UIExplorer still works.
Closes https://github.com/facebook/react-native/pull/13354

Reviewed By: bvaughn

Differential Revision: D4928785

Pulled By: javache

fbshipit-source-id: 38c623c309b06b2cb5e73074833342d2745ab198

Libraries/Utilities/throwOnWrongReactAPI.js

@@ -1,32 +0,0 @@
-/**
- * Copyright (c) 2015-present, Facebook, Inc.
- * All rights reserved.
- *
- * This source code is licensed under the BSD-style license found in the
- * LICENSE file in the root directory of this source tree. An additional grant
- * of patent rights can be found in the PATENTS file in the same directory.
- *
- * @providesModule throwOnWrongReactAPI
- * @flow
- */
-
-'use strict';
-
-function throwOnWrongReactAPI(key: string) {
-  throw new Error(
-`Seems you're trying to access 'ReactNative.${key}' from the 'react-native' package. Perhaps you meant to access 'React.${key}' from the 'react' package instead?
-
-For example, instead of:
-
-  import React, { Component, View } from 'react-native';
-
-You should now do:
-
-  import React, { Component } from 'react';
-  import { View } from 'react-native';
-
-Check the release notes on how to upgrade your code - https://github.com/facebook/react-native/releases/tag/v0.25.1
-`);
-}
-
-module.exports = throwOnWrongReactAPI;

Libraries/react-native/react-native-implementation.js

@@ -124,43 +124,4 @@ const ReactNative = {
   },
 };
 
-// Better error messages when accessing React APIs on ReactNative
-if (__DEV__) {
-  const throwOnWrongReactAPI = require('throwOnWrongReactAPI');
-  const reactAPIs = [ 'createClass', 'Component' ];
-
-  for (const key of reactAPIs) {
-    Object.defineProperty(ReactNative, key, {
-      get() { throwOnWrongReactAPI(key); },
-      enumerable: false,
-      configurable: false,
-    });
-  }
-}
-
-// Preserve getters with warnings on the internal ReactNative copy without
-// invoking them.
-const ReactNativeInternal = require('ReactNative');
-function applyForwarding(key) {
-  if (__DEV__) {
-    Object.defineProperty(
-      ReactNative,
-      key,
-      Object.getOwnPropertyDescriptor(ReactNativeInternal, key)
-    );
-    return;
-  }
-    if (ReactNative.hasOwnProperty(key)) {
-      // WARNING! ReactNative has read-only keys. So, if ReactNativeInternal
-      // has any duplicate key that ReactNative already has, this assignment
-      // would fail with "Attempted to assign to readonly property."
-      // So, if the key already exists on ReactNative, we assume that it's the
-      // correct module and skip re-assigning it.
-      return;
-    }
-  ReactNative[key] = ReactNativeInternal[key];
-}
-for (const key in ReactNativeInternal) {
-  applyForwarding(key);
-}
 module.exports = ReactNative;