Fix RNTester Not Resizing Examples on Rotation/Resize (#30376)

Summary:
Fixes #30325

After the RNTester redesign, a style started globally caching screen width. This isn't needed, but means that width is incorrect if the device is rotated, or a window is resized. Rely on default layout which will be 100% width instead.
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[Internal] [Fixed] - Fix RNTester Not Resizing Examples on Rotation/Resize

Pull Request resolved: #30376

Test Plan: Tested viewing an example and rotating the device in iOS simulator

Reviewed By: rickhanlonii

Differential Revision: D25098642

Pulled By: appden

fbshipit-source-id: 9acdb656da7de9fda05f6091b36f8d9aa2155524

packages/rn-tester/js/components/ExamplePage.js

@@ -11,7 +11,7 @@
 'use strict';
 
 import * as React from 'react';
-import {StyleSheet, View, Text, Dimensions} from 'react-native';
+import {StyleSheet, View, Text} from 'react-native';
 
 type Props = $ReadOnly<{|
   children?: React.Node,
@@ -22,7 +22,6 @@ type Props = $ReadOnly<{|
   android?: ?boolean,
 |}>;
 
-const ScreenWidth = Dimensions.get('window').width;
 import {RNTesterThemeContext} from './RNTesterTheme';
 
 export default function ExamplePage(props: Props): React.Node {
@@ -76,7 +75,6 @@ const styles = StyleSheet.create({
     justifyContent: 'flex-end',
   },
   examplesContainer: {
-    width: ScreenWidth,
     flexGrow: 1,
   },
   description: {