Remove use of '--enable-isolate-groups' dart vm flag. (#30839)
Remove use of '--enable-isolate-groups' dart vm flag. (#30839)

The flag was removed after isolate groups were enabled by default.

Fixes https://github.com/flutter/flutter/issues/95331
flutter/engine,rmacnak-google/engine,jason-simmons/flutter_engine,chinmaygarde/flutter_engine,devoncarew/engine,flutter/engine,devoncarew/engine,chinmaygarde/flutter_engine,jason-simmons/flutter_engine,flutter/engine,jason-simmons/flutter_engine,chinmaygarde/flutter_engine,devoncarew/engine,rmacnak-google/engine,jason-simmons/flutter_engine,devoncarew/engine,jason-simmons/flutter_engine,rmacnak-google/engine,devoncarew/engine,chinmaygarde/flutter_engine,jason-simmons/flutter_engine,devoncarew/engine,jason-simmons/flutter_engine,flutter/engine,rmacnak-google/engine,chinmaygarde/flutter_engine,chinmaygarde/flutter_engine,rmacnak-google/engine,flutter/engine,flutter/engine,flutter/engine,rmacnak-google/engine,jason-simmons/flutter_engine,rmacnak-google/engine,flutter/engine,chinmaygarde/flutter_engine,devoncarew/engine