Remove a few unnecessary includes

Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/6046

Test Plan: make check, manual inspection

Differential Revision: D18573044

Pulled By: pdillinger

fbshipit-source-id: 7a5999fc08d798ce3157b56d4b36d24027409fc3

table/plain/plain_table_index.h

@@ -15,8 +15,6 @@
 #include "monitoring/histogram.h"
 #include "options/cf_options.h"
 #include "rocksdb/options.h"
-#include "util/hash.h"
-#include "util/murmurhash.h"
 
 namespace rocksdb {
 

table/plain/plain_table_reader.cc

@@ -36,7 +36,6 @@
 #include "util/coding.h"
 #include "util/dynamic_bloom.h"
 #include "util/hash.h"
-#include "util/murmurhash.h"
 #include "util/stop_watch.h"
 #include "util/string_util.h"