blink_gc_plugin: retire overloaded traceImpl detection and handling.

tools/clang/blink_gc_plugin/tests/traceimpl_derived_from_templated_base.h

 // Copyright 2015 The Chromium 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 TRACEIMPL_DERIVED_FROM_TEMPLATED_BASE_H_
 #define TRACEIMPL_DERIVED_FROM_TEMPLATED_BASE_H_
 
 #include "heap/stubs.h"
 
 namespace blink {
 
 class X : public GarbageCollected<X> {
  public:
   virtual void Trace(Visitor*) {}
 };
 
 template <int Y>
 class TraceImplTemplatedBase
     : public GarbageCollected<TraceImplTemplatedBase<Y> > {
  public:
-  void Trace(Visitor* visitor) { TraceImpl(visitor); }
-
-  template <typename VisitorDispatcher>
-  void TraceImpl(VisitorDispatcher visitor) {
-    visitor->Trace(x_);
-  }
+  void Trace(Visitor* visitor) { visitor->Trace(x_); }
 
  private:
   Member<X> x_;
 };
 
 class TraceImplDerivedFromTemplatedBase : public TraceImplTemplatedBase<0> {
 };
 
 }
 
 #endif  // TRACEIMPL_DERIVED_FROM_TEMPLATED_BASE_H_