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/gyp/bench.gyp b/gyp/bench.gyp
index 6ec972f..15927e6 100644
--- a/gyp/bench.gyp
+++ b/gyp/bench.gyp
@@ -18,11 +18,11 @@
         'skia_lib.gyp:skia_lib',
       ],
       'sources': [
+        '../bench/BenchLogger.cpp',
+        '../bench/BenchLogger.h',
+        '../bench/GMBench.cpp',
+        '../bench/GMBench.h',
         '../bench/ResultsWriter.cpp',
-        '../bench/SkBenchLogger.cpp',
-        '../bench/SkBenchLogger.h',
-        '../bench/SkGMBench.cpp',
-        '../bench/SkGMBench.h',
         '../bench/benchmain.cpp',
         '../tools/sk_tool_utils.cpp',
       ],