Dart 3 cleanup: remove prefer_const_constructors ignores

Once https://github.com/dart-lang/sdk/issues/51800 is resolved we should remove the workarounds put in place for it by reverting the change in this commit: https://github.com/flutter/flutter/pull/122546/commits/0e0b471d0e723da161618807cd66746743b8e4bf