kv/MemDB: remove duplicated using statement of std::string

MemDB.h has already done such thing.

Signed-off-by: xie xingguo <xie.xingguo@zte.com.cn>

diff --git a/src/kv/MemDB.cc b/src/kv/MemDB.cc
index d02f7043b5ec5be6c2cf96830f556696f7230d0d..ce6c5ef952c54f1ab73b2c5364430895edee27be 100644 (file)
--- a/src/kv/MemDB.cc
+++ b/src/kv/MemDB.cc
@@ -14,7 +14,6 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 
-using std::string;
 #include "common/perf_counters.h"
 #include "common/debug.h"
 #include "include/str_list.h"