Remove the deprecated `isIPhoneX_deprecated` constant (#19920)

Summary:
Cleanup the `isIPhoneX_deprecated` constant which was said to be removed by June 1st 2018.
Closes https://github.com/facebook/react-native/pull/19920

Differential Revision: D8714400

Pulled By: hramos

fbshipit-source-id: 0b0b3a2d7b8098baf0474afea230780c79b2fe14

RNTester/js/SafeAreaViewExample.js

@@ -64,21 +64,6 @@ class SafeAreaViewExample extends React.Component<
   }
 }
 
-class IsIPhoneXExample extends React.Component<{}> {
-  render() {
-    return (
-      <View>
-        <Text>
-          Is this an iPhone X:{' '}
-          {DeviceInfo.isIPhoneX_deprecated
-            ? 'Yeah!'
-            : 'Nope. (Or `isIPhoneX_deprecated` was already removed.)'}
-        </Text>
-      </View>
-    );
-  }
-}
-
 exports.examples = [
   {
     title: '<SafeAreaView> Example',
@@ -86,15 +71,6 @@ exports.examples = [
       'SafeAreaView automatically applies paddings reflect the portion of the view that is not covered by other (special) ancestor views.',
     render: () => <SafeAreaViewExample />,
   },
-  {
-    title: 'isIPhoneX_deprecated Example',
-    description:
-      '`DeviceInfo.isIPhoneX_deprecated` returns true only on iPhone X. ' +
-      'Note: This prop is deprecated and will be removed right after June 01, 2018. ' +
-      'Please use this only for a quick and temporary solution. ' +
-      'Use <SafeAreaView> instead.',
-    render: () => <IsIPhoneXExample />,
-  },
 ];
 
 var styles = StyleSheet.create({

React/Modules/RCTDeviceInfo.m

@@ -51,22 +51,6 @@ RCT_EXPORT_MODULE()
 #endif
 }
 
-static BOOL RCTIsIPhoneX() {
-  static BOOL isIPhoneX = NO;
-  static dispatch_once_t onceToken;
-
-  dispatch_once(&onceToken, ^{
-    RCTAssertMainQueue();
-
-    isIPhoneX = CGSizeEqualToSize(
-      [UIScreen mainScreen].nativeBounds.size,
-      CGSizeMake(1125, 2436)
-    );
-  });
-
-  return isIPhoneX;
-}
-
 static NSDictionary *RCTExportedDimensions(RCTBridge *bridge)
 {
   RCTAssertMainQueue();
@@ -102,11 +86,6 @@ static NSDictionary *RCTExportedDimensions(RCTBridge *bridge)
 {
   return @{
     @"Dimensions": RCTExportedDimensions(_bridge),
-    // Note:
-    // This prop is deprecated and will be removed right after June 01, 2018.
-    // Please use this only for a quick and temporary solution.
-    // Use <SafeAreaView> instead.
-    @"isIPhoneX_deprecated": @(RCTIsIPhoneX()),
   };
 }