Remove the ability in dart2js to turn off syntax-only generic methods.

pkg/compiler/lib/src/dart2js.dart

Index: pkg/compiler/lib/src/dart2js.dart
diff --git a/pkg/compiler/lib/src/dart2js.dart b/pkg/compiler/lib/src/dart2js.dart
index 352fc9f9802582e3aad678cf5929c3b20851e265..d900eb0b7e0f8251316fa6f581f2df5f66dc2988 100644
--- a/pkg/compiler/lib/src/dart2js.dart
+++ b/pkg/compiler/lib/src/dart2js.dart
@@ -138,6 +138,8 @@ Future<api.CompilationResult> compile(List<String> argv) {
 
   void passThrough(String argument) => options.add(argument);
 
+  void ignoreOption(String argument) {}
+
   if (BUILD_ID != null) {
     passThrough("--build-id=$BUILD_ID");
   }
@@ -332,7 +334,7 @@ Future<api.CompilationResult> compile(List<String> argv) {
     new OptionHandler('--out=.+|-o.*', setOutput, multipleArguments: true),
     new OptionHandler(Flags.allowMockCompilation, passThrough),
     new OptionHandler(Flags.fastStartup, passThrough),
-    new OptionHandler(Flags.genericMethodSyntax, passThrough),
+    new OptionHandler(Flags.genericMethodSyntax, ignoreOption),
     new OptionHandler(Flags.initializingFormalAccess, passThrough),
     new OptionHandler('${Flags.minify}|-m', implyCompilation),
     new OptionHandler(Flags.preserveUris, passThrough),