fix #29544, mixins to a class with named constructors

pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/rtti.dart

Index: pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/rtti.dart
diff --git a/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/rtti.dart b/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/rtti.dart
index fc156363c3dd7b4b305b8798a3296115612e1b2f..fd7c515c1558a770065cd566f2ebf47feea6a330 100644
--- a/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/rtti.dart
+++ b/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/rtti.dart
@@ -72,7 +72,6 @@ lazyFn(closure, computeType) {
 
 // TODO(vsm): How should we encode the runtime type?
 final _runtimeType = JS('', 'Symbol("_runtimeType")');
-final isNamedConstructor = JS('', 'Symbol("isNamedConstructor")');
 
 final _moduleName = JS('', 'Symbol("_moduleName")');
 
@@ -188,7 +187,6 @@ lazyAnonymousJSType(name) {
 unwrapType(WrappedType obj) => obj._wrappedType;
 
 _getRuntimeType(value) => JS('', '#[#]', value, _runtimeType);
-getIsNamedConstructor(value) => JS('', '#[#]', value, isNamedConstructor);
 
 /// Return the module name for a raw library object.
 getModuleName(value) => JS('', '#[#]', value, _moduleName);