[dart2js, ddc] Remove LEGACY support from rti.

- Remove support for `JS_GET_FLAG('LEGACY')` from backends
- Remove `kindStar` Rtis
- Remove `Recipe.wrapStar`

Bug: #60327
Change-Id: I2ec9b0afc9f3cd99fc6167600e6d908c9771af1d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/416101
Reviewed-by: Nicholas Shahan <nshahan@google.com>
Reviewed-by: Stephen Adams <sra@google.com>
Reviewed-by: Nate Biggs <natebiggs@google.com>

pkg/js_shared/lib/synced/recipe_syntax.dart

@@ -28,8 +28,6 @@ abstract class Recipe {
   static const int pushVoid = _tilde;
   static const String pushVoidString = _tildeString;
 
-  static const int wrapStar = _asterisk;
-  static const String wrapStarString = _asteriskString;
   static const int wrapQuestion = _question;
   static const String wrapQuestionString = _questionString;
   static const int wrapFutureOr = _slash;
@@ -187,7 +185,6 @@ abstract class Recipe {
     test("pushErased", pushErased, pushErasedString);
     test("pushDynamic", pushDynamic, pushDynamicString);
     test("pushVoid", pushVoid, pushVoidString);
-    test("wrapStar", wrapStar, wrapStarString);
     test("wrapQuestion", wrapQuestion, wrapQuestionString);
     test("wrapFutureOr", wrapFutureOr, wrapFutureOrString);
     test("startTypeArguments", startTypeArguments, startTypeArgumentsString);