uiscene_plugin_lifecycle_test_ios: AppNotMigrated scenarios crash on launch with Xcode 27 #194513

1. Install Xcode 27 +
2. From dev/devicelab run dart bin/run.dart -t uiscene_plugin_lifecycle_test_ios

The four AppMigrated-* scenarios pass. The AppNotMigrated-* scenario fails (expectedly) because the host app is killed at launch since it's not migrated to UIScene.

We could:

• Skip these scenarios when the selected Xcode is 27 or newer
• Remove these cases totally

I don't think it makes sense to "validate" it's crashing since that's just testing iOS's behavior. This is a native add-to-app host app so there's nothing flutter in there to validate there's an actionable message.

Previously undiscovered because the app wasn't launching due to #194147.

This is blocking Xcode 27 in CI.