[builtins] Remove STRING_ADD_LEFT and STRING_ADD_RIGHT builtins.

src/objects.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_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 
 #include "src/allocation.h"
@@ skipping 5772 matching lines @@
   static const int kIsCallable = 1;
   static const int kHasNamedInterceptor = 2;
   static const int kHasIndexedInterceptor = 3;
   static const int kIsUndetectable = 4;
   static const int kIsObserved = 5;
   static const int kIsAccessCheckNeeded = 6;
   class FunctionWithPrototype: public BitField<bool, 7,  1> {};
 
   // Bit positions for bit field 2
   static const int kIsExtensible = 0;
-  static const int kStringWrapperSafeForDefaultValueOf = 1;
+  // Bit 1 is free.
   class IsPrototypeMapBits : public BitField<bool, 2, 1> {};
   class ElementsKindBits: public BitField<ElementsKind, 3, 5> {};
 
   // Derived values from bit field 2
   static const int8_t kMaximumBitField2FastElementValue = static_cast<int8_t>(
       (FAST_ELEMENTS + 1) << Map::ElementsKindBits::kShift) - 1;
   static const int8_t kMaximumBitField2FastSmiElementValue =
       static_cast<int8_t>((FAST_SMI_ELEMENTS + 1) <<
                           Map::ElementsKindBits::kShift) - 1;
   static const int8_t kMaximumBitField2FastHoleyElementValue =
@@ skipping 4662 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_