Remove Sk prefix from some bench classes.

This idea came while commenting on
https://codereview.chromium.org/343583005/

Since SkBenchmark, SkBenchLogger and SkGMBench are not part of the Skia library,
they should not have the Sk prefix.

BUG=None
TEST=make all
R=mtklein@google.com

Author: tfarina@chromium.org

Review URL: https://codereview.chromium.org/347823004
diff --git a/bench/PerlinNoiseBench.cpp b/bench/PerlinNoiseBench.cpp
index ff0baf3..560628f 100644
--- a/bench/PerlinNoiseBench.cpp
+++ b/bench/PerlinNoiseBench.cpp
@@ -4,11 +4,11 @@
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
-#include "SkBenchmark.h"
+#include "Benchmark.h"
 #include "SkCanvas.h"
 #include "SkPerlinNoiseShader.h"
 
-class PerlinNoiseBench : public SkBenchmark {
+class PerlinNoiseBench : public Benchmark {
     SkISize fSize;
 
 public:
@@ -54,7 +54,7 @@
         }
     }
 
-    typedef SkBenchmark INHERITED;
+    typedef Benchmark INHERITED;
 };
 
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