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/FSRectBench.cpp b/bench/FSRectBench.cpp
index ea65f30..3c53042 100644
--- a/bench/FSRectBench.cpp
+++ b/bench/FSRectBench.cpp
@@ -6,7 +6,7 @@
  * found in the LICENSE file.
  */
 
-#include "SkBenchmark.h"
+#include "Benchmark.h"
 #include "SkCanvas.h"
 #include "SkPaint.h"
 #include "SkRandom.h"
@@ -15,7 +15,7 @@
  * Draws full screen opaque rectangles. It is designed to test any optimizations in the GPU backend
  * to turn such draws into clears.
  */
-class FSRectBench : public SkBenchmark {
+class FSRectBench : public Benchmark {
 public:
     FSRectBench() : fInit(false) { }
 
@@ -57,7 +57,7 @@
     SkColor fColors[N];
     bool fInit;
 
-    typedef SkBenchmark INHERITED;
+    typedef Benchmark INHERITED;
 };
 
 DEF_BENCH( return SkNEW_ARGS(FSRectBench, ()); )