[Tracing] Remove unused variable kRuntimeCallStatsTracingEnabled.

src/tracing/trace-event.h

 // Copyright 2015 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 SRC_TRACING_TRACE_EVENT_H_
 #define SRC_TRACING_TRACE_EVENT_H_
 
 #include <stddef.h>
 #include <memory>
 
@@ skipping 257 matching lines @@
 class Isolate;
 
 namespace tracing {
 
 // Specify these values when the corresponding argument of AddTraceEvent is not
 // used.
 const int kZeroNumArgs = 0;
 const decltype(nullptr) kGlobalScope = nullptr;
 const uint64_t kNoId = 0;
 
-extern base::Atomic32 kRuntimeCallStatsTracingEnabled;
-
 class TraceEventHelper {
  public:
   static v8::Platform* GetCurrentPlatform();
 };
 
 // TraceID encapsulates an ID that can either be an integer or pointer. Pointers
 // are by default mangled with the Process ID so that they are unlikely to
 // collide when the same pointer is used on different processes.
 class TraceID {
  public:
@@ skipping 303 matching lines @@
   bool has_parent_scope_;
   Data* p_data_;
   Data data_;
 };
 
 }  // namespace tracing
 }  // namespace internal
 }  // namespace v8
 
 #endif  // SRC_TRACING_TRACE_EVENT_H_