clean up more dead code

src/core/SkTaskGroup.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkTaskGroup_DEFINED
 #define SkTaskGroup_DEFINED
 
 #include <functional>
 
 #include "SkTypes.h"
 #include "SkAtomics.h"
 #include "SkTemplates.h"
 
-struct SkRunnable;
-
 class SkTaskGroup : SkNoncopyable {
 public:
     // Create one of these in main() to enable SkTaskGroups globally.
     struct Enabler : SkNoncopyable {
         explicit Enabler(int threads = -1);  // Default is system-reported core count.
         ~Enabler();
     };
 
     SkTaskGroup();
     ~SkTaskGroup() { this->wait(); }
 
     // Add a task to this SkTaskGroup.  It will likely run on another thread.
-    // Neither add() method takes owership of any of its parameters.
-    void add(SkRunnable*);
-
     void add(std::function<void(void)> fn);
 
     // Add a batch of N tasks, all calling fn with different arguments.
     void batch(int N, std::function<void(int)> fn);
 
     // Block until all Tasks previously add()ed to this SkTaskGroup have run.
     // You may safely reuse this SkTaskGroup after wait() returns.
     void wait();
 
 private:
     SkAtomic<int32_t> fPending;
 };
 
 // Returns best estimate of number of CPU cores available to use.
 int sk_num_cores();
 
 #endif//SkTaskGroup_DEFINED