"Convert Enums to Strings in Dart" tip is out of date

[orevial]

This tip : https://github.com/vandadnp/flutter-tips-and-tricks/blob/main/tipsandtricks/convert-enums-to-strings-in-dart/convert-enums-to-strings-in-dart.md

is out of date because we now have enumValue.name since Dart 2.15 so I think this tip can be removed 😉