Remove unnecessary 'using' directive
am: 928facdec9

Change-Id: I9f3c658200d120229cce400562aa97d9b49539d8
diff --git a/gatekeeper_messages.cpp b/gatekeeper_messages.cpp
index 41972bb..d6d028d 100644
--- a/gatekeeper_messages.cpp
+++ b/gatekeeper_messages.cpp
@@ -19,8 +19,6 @@
 
 #include <string.h>
 
-using namespace std;
-
 namespace gatekeeper {
 
 /**