[runtime] Remove obsolete %_StringAdd intrinsic.

src/full-codegen/arm/full-codegen-arm.cc

Index: src/full-codegen/arm/full-codegen-arm.cc
diff --git a/src/full-codegen/arm/full-codegen-arm.cc b/src/full-codegen/arm/full-codegen-arm.cc
index 0e77efe0de128edebe60af1930ab035add047999..23cbe8f53e251c404864c92256d1f3e0c9cb0c99 100644
--- a/src/full-codegen/arm/full-codegen-arm.cc
+++ b/src/full-codegen/arm/full-codegen-arm.cc
@@ -3833,19 +3833,6 @@ void FullCodeGenerator::EmitStringCharAt(CallRuntime* expr) {
 }
 
 
-void FullCodeGenerator::EmitStringAdd(CallRuntime* expr) {
-  ZoneList<Expression*>* args = expr->arguments();
-  DCHECK_EQ(2, args->length());
-  VisitForStackValue(args->at(0));
-  VisitForAccumulatorValue(args->at(1));
-
-  __ pop(r1);
-  StringAddStub stub(isolate(), STRING_ADD_CHECK_BOTH, NOT_TENURED);
-  __ CallStub(&stub);
-  context()->Plug(r0);
-}
-
-
 void FullCodeGenerator::EmitCall(CallRuntime* expr) {
   ZoneList<Expression*>* args = expr->arguments();
   DCHECK_LE(2, args->length());