rand dart fix

deprecated/fb_auth/example/lib/main.dart

@@ -35,7 +35,7 @@ class _MyAppState extends State<MyApp> {
   @override
   void dispose() {
     _auth.close();
-    _userChanged?.cancel();
+    _userChanged.cancel();
     super.dispose();
   }
 

deprecated/fb_auth/example/lib/plugins/desktop/io.dart

@@ -1,19 +1,8 @@
-import 'dart:io';
 
 import 'package:flutter/foundation.dart';
-import 'package:flutter/material.dart';
 
 void setTargetPlatformForDesktop({TargetPlatform platform}) {
   TargetPlatform targetPlatform;
-  if (platform != null) {
-    targetPlatform = platform;
-  }
-  if (targetPlatform == null) {
-    if (Platform.isMacOS) {
-      targetPlatform = TargetPlatform.iOS;
-    } else if (Platform.isLinux || Platform.isWindows) {
-      targetPlatform = TargetPlatform.android;
-    }
-  }
+  targetPlatform = platform;
   debugDefaultTargetPlatformOverride = targetPlatform;
 }