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/MemsetBench.cpp b/bench/MemsetBench.cpp
index bfdff5cb..6a1bd24 100644
--- a/bench/MemsetBench.cpp
+++ b/bench/MemsetBench.cpp
@@ -5,12 +5,12 @@
  * found in the LICENSE file.
  */
 
-#include "SkBenchmark.h"
+#include "Benchmark.h"
 #include "SkCanvas.h"
-#include "SkUtils.h"
 #include "SkString.h"
+#include "SkUtils.h"
 
-class MemsetBench : public SkBenchmark {
+class MemsetBench : public Benchmark {
     SkString    fName;
 
 protected:
@@ -54,7 +54,7 @@
     }
 
 private:
-    typedef SkBenchmark INHERITED;
+    typedef Benchmark INHERITED;
 };
 
 class Memset32Bench : public MemsetBench {