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/DisplacementBench.cpp b/bench/DisplacementBench.cpp
index 904f47d..881ba33 100644
--- a/bench/DisplacementBench.cpp
+++ b/bench/DisplacementBench.cpp
@@ -4,7 +4,7 @@
  * 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 "SkBitmapDevice.h"
 #include "SkBitmapSource.h"
 #include "SkCanvas.h"
@@ -15,7 +15,7 @@
 #define FILTER_WIDTH_LARGE  256
 #define FILTER_HEIGHT_LARGE 256
 
-class DisplacementBaseBench : public SkBenchmark {
+class DisplacementBaseBench : public Benchmark {
 public:
     DisplacementBaseBench(bool small) :
         fInitialized(false), fIsSmall(small) {
@@ -82,7 +82,7 @@
 private:
     bool fInitialized;
     bool fIsSmall;
-    typedef SkBenchmark INHERITED;
+    typedef Benchmark INHERITED;
 };
 
 class DisplacementZeroBench : public DisplacementBaseBench {