Cleanup unnecessary duplication of runtime functions.

src/hydrogen.cc

Index: src/hydrogen.cc
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index 7342b401563062d66a7a157f9c1175e9ddcf5467..794a38b8e4d4faa0f703c5e520fdc69e6c734e60 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -2505,7 +2505,7 @@ HValue* HGraphBuilder::BuildUncheckedStringAdd(
       // Fallback to the runtime to add the two strings.
       Add<HPushArguments>(left, right);
       Push(Add<HCallRuntime>(isolate()->factory()->empty_string(),
-                             Runtime::FunctionForId(Runtime::kStringAddRT), 2));
+                             Runtime::FunctionForId(Runtime::kStringAdd), 2));
     }
     if_sameencodingandsequential.End();
   }