[runtime] Remove obsolete %_StringAdd intrinsic.

src/full-codegen/full-codegen.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_FULL_CODEGEN_FULL_CODEGEN_H_
 #define V8_FULL_CODEGEN_FULL_CODEGEN_H_
 
 #include "src/allocation.h"
 #include "src/assert-scope.h"
 #include "src/ast.h"
@@ skipping 486 matching lines @@
   F(MathPow)                            \
   F(IsMinusZero)                        \
   F(HasCachedArrayIndex)                \
   F(GetCachedArrayIndex)                \
   F(FastOneByteArrayJoin)               \
   F(GeneratorNext)                      \
   F(GeneratorThrow)                     \
   F(DebugBreakInOptimizedCode)          \
   F(ClassOf)                            \
   F(StringCharCodeAt)                   \
-  F(StringAdd)                          \
   F(SubString)                          \
   F(RegExpExec)                         \
   F(RegExpConstructResult)              \
   F(ToInteger)                          \
   F(NumberToString)                     \
   F(ToString)                           \
   F(ToLength)                           \
   F(ToNumber)                           \
   F(ToName)                             \
   F(ToObject)                           \
@@ skipping 528 matching lines @@
   Address start_;
   Address instruction_start_;
   uint32_t length_;
 };
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_FULL_CODEGEN_FULL_CODEGEN_H_