Remove support for mixin typedefs in dart2js.

pkg/compiler/lib/src/resolution/class_hierarchy.dart

Index: pkg/compiler/lib/src/resolution/class_hierarchy.dart
diff --git a/pkg/compiler/lib/src/resolution/class_hierarchy.dart b/pkg/compiler/lib/src/resolution/class_hierarchy.dart
index 551a47e7332bbed9323fa1546f0b3ac578d0b1dc..b9fae9797b3619b4e8b296fa5f04ee2ef5fb62bb 100644
--- a/pkg/compiler/lib/src/resolution/class_hierarchy.dart
+++ b/pkg/compiler/lib/src/resolution/class_hierarchy.dart
@@ -276,13 +276,6 @@ class ClassResolverVisitor extends TypeDefinitionVisitor {
           element, 'cyclic resolution of class $element');
     }
 
-    if (identical(node.classKeyword.stringValue, 'typedef')) {
-      // TODO(aprelev@gmail.com): Remove this deprecation diagnostic
-      // together with corresponding TODO in parser.dart.
-      reporter.reportWarningMessage(
-          node.classKeyword, MessageKind.DEPRECATED_TYPEDEF_MIXIN_SYNTAX);
-    }
-
     element.computeType(resolution);
     scope = new TypeDeclarationScope(scope, element);
     resolveTypeVariableBounds(node.typeParameters);