Delete dead subset benches from nanobench

bench/subset/SubsetSingleBench.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Benchmark.h"
 #include "SkImageDecoder.h"
 #include "SkImageInfo.h"
 #include "SkStream.h"
 #include "SkString.h"
 
 /*
  *
  * This benchmark is designed to test the performance of subset decoding.
  * It uses an input width, height, left, and top to decode a single subset.
  *
  */
 class SubsetSingleBench : public Benchmark {
 public:
 
     SubsetSingleBench(const SkString& path,
                       SkColorType colorType,
                       uint32_t subsetWidth,
                       uint32_t subsetHeight,
                       uint32_t offsetLeft,
-                      uint32_t offsetTop,
-                      bool useCodec);
+                      uint32_t offsetTop);
 
 protected:
     const char* onGetName() override;
     bool isSuitableFor(Backend backend) override;
     void onDraw(int n, SkCanvas* canvas) override;
 
 private:
     SkString                      fName;
     SkColorType                   fColorType;
     const uint32_t                fSubsetWidth;
     const uint32_t                fSubsetHeight;
     const uint32_t                fOffsetLeft;
     const uint32_t                fOffsetTop;
-    const bool                    fUseCodec;
     SkAutoTDelete<SkMemoryStream> fStream;
     typedef Benchmark INHERITED;
 };