Delete dart2js specific private library code

lib/runtime/dart/core.js

Index: lib/runtime/dart/core.js
diff --git a/lib/runtime/dart/core.js b/lib/runtime/dart/core.js
index 1eac80377c7c89eab07b7075358d231fc00895a9..ab265f1279a34aa2d00076f7749411e6b410cf45 100644
--- a/lib/runtime/dart/core.js
+++ b/lib/runtime/dart/core.js
@@ -58,12 +58,12 @@ var convert = dart.lazyImport(convert);
   dart.setSignature(JsPeerInterface, {
     constructors: () => ({JsPeerInterface: [JsPeerInterface, [], {name: String}]})
   });
-  class SupportJsExtensionMethod extends Object {
-    SupportJsExtensionMethod() {
+  class SupportJsExtensionMethods extends Object {
+    SupportJsExtensionMethods() {
     }
   }
-  dart.setSignature(SupportJsExtensionMethod, {
-    constructors: () => ({SupportJsExtensionMethod: [SupportJsExtensionMethod, []]})
+  dart.setSignature(SupportJsExtensionMethods, {
+    constructors: () => ({SupportJsExtensionMethods: [SupportJsExtensionMethods, []]})
   });
   class Deprecated extends Object {
     Deprecated(expires) {
@@ -3738,13 +3738,6 @@ var convert = dart.lazyImport(convert);
     return result;
   }
   dart.fn(_symbolMapToStringMap, Object, [Map$(Symbol, Object)]);
-  class SupportJsExtensionMethods extends Object {
-    SupportJsExtensionMethods() {
-    }
-  }
-  dart.setSignature(SupportJsExtensionMethods, {
-    constructors: () => ({SupportJsExtensionMethods: [SupportJsExtensionMethods, []]})
-  });
   class _ListConstructorSentinel extends Object {
     _ListConstructorSentinel() {
     }
@@ -3756,7 +3749,7 @@ var convert = dart.lazyImport(convert);
   exports.Object = Object;
   exports.JsName = JsName;
   exports.JsPeerInterface = JsPeerInterface;
-  exports.SupportJsExtensionMethod = SupportJsExtensionMethod;
+  exports.SupportJsExtensionMethods = SupportJsExtensionMethods;
   exports.Deprecated = Deprecated;
   exports.deprecated = deprecated;
   exports.override = override;
@@ -3881,5 +3874,4 @@ var convert = dart.lazyImport(convert);
   exports.Symbol = Symbol;
   exports.Type = Type;
   exports.Uri = Uri;
-  exports.SupportJsExtensionMethods = SupportJsExtensionMethods;
 })(core, _js_helper, _internal, collection, _interceptors, math, convert);