Refactoring: get rid of the SkBenchmark void* parameter.

bench/benchmain.cpp

Index: bench/benchmain.cpp
diff --git a/bench/benchmain.cpp b/bench/benchmain.cpp
index 289d5cb0a24a03e4264b215244865b44dc920385..412e14d4da5044c0e15ea1732e4df16ab2463e85 100644
--- a/bench/benchmain.cpp
+++ b/bench/benchmain.cpp
@@ -56,7 +56,7 @@ public:
         if (fBench) {
             BenchRegistry::Factory f = fBench->factory();
             fBench = fBench->next();
-            return f(NULL);
+            return f();
         }
         return NULL;
     }