Fix broken integration test for streaming

The `whenComplete` call was sometimes causing a race condition. It is also isn't needed for the test (to reset the value of isDetecting, given it's local), so removing it makes the test reliable.

packages/camera/camera_android/example/integration_test/camera_test.dart

@@ -272,7 +272,7 @@ void main() {
 
         isDetecting = true;
 
-        expectLater(image, isNotNull).whenComplete(() => isDetecting = false);
+        expectLater(image, isNotNull);
       });
 
       expect(controller.value.isStreamingImages, true);