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/FontScalerBench.cpp b/bench/FontScalerBench.cpp
index a14723c..0326a0c 100644
--- a/bench/FontScalerBench.cpp
+++ b/bench/FontScalerBench.cpp
@@ -5,14 +5,14 @@
  * found in the LICENSE file.
  */
 
-#include "SkBenchmark.h"
+#include "Benchmark.h"
 #include "SkCanvas.h"
 #include "SkGraphics.h"
 #include "SkPaint.h"
 #include "SkRandom.h"
 #include "SkString.h"
 
-class FontScalerBench : public SkBenchmark {
+class FontScalerBench : public Benchmark {
     SkString fName;
     SkString fText;
     bool     fDoLCD;
@@ -43,7 +43,7 @@
         }
     }
 private:
-    typedef SkBenchmark INHERITED;
+    typedef Benchmark INHERITED;
 };
 
 ///////////////////////////////////////////////////////////////////////////////