[change] Remove AlertIOS

Ref #1352
Ref https://github.com/facebook/react-native/issues/23313

packages/babel-plugin-react-native-web/src/moduleMap.js

@@ -3,7 +3,6 @@ module.exports = {
   AccessibilityInfo: true,
   ActivityIndicator: true,
   Alert: true,
-  AlertIOS: true,
   Animated: true,
   AppRegistry: true,
   AppState: true,

packages/react-native-web/src/exports/AlertIOS/index.js

@@ -1 +0,0 @@
-export default {};

packages/react-native-web/src/index.js

@@ -90,7 +90,6 @@ import ToolbarAndroid from './exports/ToolbarAndroid';
 import ViewPagerAndroid from './exports/ViewPagerAndroid';
 import WebView from './exports/WebView';
 // compat (apis)
-import AlertIOS from './exports/AlertIOS';
 import CameraRoll from './exports/CameraRoll';
 import DatePickerAndroid from './exports/DatePickerAndroid';
 import ImagePickerIOS from './exports/ImagePickerIOS';
@@ -197,7 +196,6 @@ export {
   ViewPagerAndroid,
   WebView,
   // compat (apis)
-  AlertIOS,
   CameraRoll,
   DatePickerAndroid,
   ImagePickerIOS,