rocksdb: Remove #include "util/random.h" from util/testharness.h

Summary: Cleaning util/testharness.h

Test Plan:
Make completes with no errors.
```
% make all
```

Reviewers: meyering, igor, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D35487

util/options_test.cc

@@ -20,6 +20,7 @@
 #include "rocksdb/utilities/convenience.h"
 #include "rocksdb/utilities/leveldb_options.h"
 #include "table/block_based_table_factory.h"
+#include "util/random.h"
 #include "util/testharness.h"
 
 #ifndef GFLAGS

util/testharness.h

@@ -13,7 +13,6 @@
 
 #include <string>
 #include "rocksdb/env.h"
-#include "util/random.h"
 #include "util/string_util.h"
 
 namespace rocksdb {