review fixes

packages/device_info/android/src/main/java/io/flutter/plugins/deviceinfo/DeviceInfoPlugin.java

@@ -30,12 +30,17 @@ public void onAttachedToEngine(FlutterPlugin.FlutterPluginBinding binding) {
 
   @Override
   public void onDetachedFromEngine(FlutterPlugin.FlutterPluginBinding binding) {
-    channel.setMethodCallHandler(null);
+    tearDownChannel();
   }
 
   private void setupMethodChannel(BinaryMessenger messenger, ContentResolver contentResolver) {
     channel = new MethodChannel(messenger, "plugins.flutter.io/device_info");
     final MethodCallHandlerImpl handler = new MethodCallHandlerImpl(contentResolver);
     channel.setMethodCallHandler(handler);
   }
+
+  private void tearDownChannel() {
+    channel.setMethodCallHandler(null);
+    channel = null;
+  }
 }

packages/device_info/example/android/app/src/main/AndroidManifest.xml

@@ -13,7 +13,6 @@
                   android:windowSoftInputMode="adjustResize">
         </activity>
         <activity android:name=".MainActivity"
-            android:launchMode="singleTop"
             android:theme="@android:style/Theme.Black.NoTitleBar"
             android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection"
             android:hardwareAccelerated="true"