[Atomics] Remove Atomics code stubs; use TF ops

src/code-factory.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_CODE_FACTORY_H_
 #define V8_CODE_FACTORY_H_
 
 #include "src/allocation.h"
 #include "src/assembler.h"
 #include "src/codegen.h"
@@ skipping 128 matching lines @@
                        TailCallMode tail_call_mode = TailCallMode::kDisallow);
   static Callable CallFunction(
       Isolate* isolate, ConvertReceiverMode mode = ConvertReceiverMode::kAny);
   static Callable Construct(Isolate* isolate);
   static Callable ConstructFunction(Isolate* isolate);
 
   static Callable InterpreterPushArgsAndCall(Isolate* isolate,
                                              TailCallMode tail_call_mode);
   static Callable InterpreterPushArgsAndConstruct(Isolate* isolate);
   static Callable InterpreterCEntry(Isolate* isolate, int result_size = 1);
-
-  static Callable AtomicsLoad(Isolate* isolate);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_CODE_FACTORY_H_