Remove legacy context API usage

Summary:
Changelog:
[General][Removed] - Remove legacy context API usage in AppContainer

Reviewed By: kacieb

Differential Revision: D27681097

fbshipit-source-id: 7391be577955171ade5b8fd53cf274900f88e7ca

Libraries/ReactNative/AppContainer.js

@@ -13,11 +13,8 @@ import RCTDeviceEventEmitter from '../EventEmitter/RCTDeviceEventEmitter';
 import StyleSheet from '../StyleSheet/StyleSheet';
 import {type EventSubscription} from '../vendor/emitter/EventEmitter';
 import {RootTagContext, createRootTag} from './RootTag';
-import PropTypes from 'prop-types';
 import * as React from 'react';
 
-type Context = {rootTag: number, ...};
-
 type Props = $ReadOnly<{|
   children?: React.Node,
   fabric?: boolean,
@@ -45,18 +42,6 @@ class AppContainer extends React.Component<Props, State> {
 
   static getDerivedStateFromError: any = undefined;
 
-  static childContextTypes:
-    | any
-    | {|rootTag: React$PropType$Primitive<number>|} = {
-    rootTag: PropTypes.number,
-  };
-
-  getChildContext(): Context {
-    return {
-      rootTag: this.props.rootTag,
-    };
-  }
-
   componentDidMount(): void {
     if (__DEV__) {
       if (!global.__RCTProfileIsProfiling) {