Fix includes in util/testharness.h.

This CL removes unused headers included by util/testharness.h, adds
precise includes where the build breaks, and fixes style errors in the
edited files.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=189331061

db/db_bench.cc

@@ -5,11 +5,10 @@
 #include <sys/types.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include "db/db_impl.h"
-#include "db/version_set.h"
 #include "leveldb/cache.h"
 #include "leveldb/db.h"
 #include "leveldb/env.h"
+#include "leveldb/filter_policy.h"
 #include "leveldb/write_batch.h"
 #include "port/port.h"
 #include "util/crc32c.h"