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/TileBench.cpp b/bench/TileBench.cpp
index 12c9629..7487b1b 100644
--- a/bench/TileBench.cpp
+++ b/bench/TileBench.cpp
@@ -6,7 +6,7 @@
  * found in the LICENSE file.
  */
 
-#include "SkBenchmark.h"
+#include "Benchmark.h"
 #include "SkBitmap.h"
 #include "SkCanvas.h"
 #include "SkShader.h"
@@ -28,7 +28,7 @@
 
 // Test out the special case of a tiled 1xN texture. Test out opacity,
 // filtering and the different tiling modes
-class ConstXTileBench : public SkBenchmark {
+class ConstXTileBench : public Benchmark {
     SkPaint             fPaint;
     SkString            fName;
     bool                fDoFilter;
@@ -111,7 +111,7 @@
     }
 
 private:
-    typedef SkBenchmark INHERITED;
+    typedef Benchmark INHERITED;
 };
 
 DEF_BENCH(return new ConstXTileBench(SkShader::kRepeat_TileMode, SkShader::kRepeat_TileMode, false, false, true))