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/DeferredCanvasBench.cpp b/bench/DeferredCanvasBench.cpp
index 6ffd2d2..667895c 100644
--- a/bench/DeferredCanvasBench.cpp
+++ b/bench/DeferredCanvasBench.cpp
@@ -4,12 +4,12 @@
  * 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 "SkDeferredCanvas.h"
 #include "SkDevice.h"
 #include "SkString.h"
 
-class DeferredCanvasBench : public SkBenchmark {
+class DeferredCanvasBench : public Benchmark {
 public:
     DeferredCanvasBench(const char name[])  {
         fName.printf("deferred_canvas_%s", name);
@@ -46,7 +46,7 @@
     SkString fName;
 
 private:
-    typedef SkBenchmark INHERITED;
+    typedef Benchmark INHERITED;
 };
 
 class SimpleNotificationClient : public SkDeferredCanvas::NotificationClient {