remove unused code

samples/simpleDemo/App.js

 
 import React, {Component} from 'react';
 import {
-  Platform, StyleSheet, Text, View, TouchableOpacity, TextInput
+  StyleSheet, Text, View, TouchableOpacity, TextInput
 } from 'react-native';
 import AgoraRTCView from './components/agora';
 
-const instructions = Platform.select({
-  ios: 'Press Cmd+R to reload,\n' + 'Cmd+D or shake for dev menu',
-  android:
-    'Double tap R on your keyboard to reload,\n' +
-    'Shake or press menu button for dev menu',
-});
-
 const styles = StyleSheet.create({
   container: {
     flex: 1,