Remove Sk prefix from some bench classes.

gyp/bench.gypi

 {
   'include_dirs': [
     '../src/core',
     '../src/effects',
     '../src/utils',
     '../tools',
   ],
   'dependencies': [
     'skia_lib.gyp:skia_lib',
   ],
   'sources': [
-    '../bench/SkBenchmark.cpp',
-    '../bench/SkBenchmark.h',
+    '../bench/Benchmark.cpp',
+    '../bench/Benchmark.h',
 
     '../bench/AAClipBench.cpp',
     '../bench/BicubicBench.cpp',
     '../bench/BitmapBench.cpp',
     '../bench/BitmapRectBench.cpp',
     '../bench/BitmapScaleBench.cpp',
     '../bench/BlurBench.cpp',
     '../bench/BlurImageFilterBench.cpp',
     '../bench/BlurRectBench.cpp',
     '../bench/BlurRoundRectBench.cpp',
@@ skipping 61 matching lines @@
     '../bench/StrokeBench.cpp',
     '../bench/TableBench.cpp',
     '../bench/TextBench.cpp',
     '../bench/TileBench.cpp',
     '../bench/VertBench.cpp',
     '../bench/WritePixelsBench.cpp',
     '../bench/WriterBench.cpp',
     '../bench/XfermodeBench.cpp',
   ],
 }