scenario_app repeatedly prints out warnings that FlutterJNI.init and others are called more than once

We end up in this code block: https://github.com/flutter/engine/blob/766a5144eed33b0f048e5e20c2bfdf798b3470d4/shell/platform/android/io/flutter/embedding/engine/FlutterEngine.java#L352-L355

I think it's probably because of how test cases are running. I'm not sure of the best way to fix this.