Cleanup to DECLARE_string in header file, and make sure dependency is clearer.

Change-Id: I103575ef6d56a3f50da0c60ca44aacb3f02194e9
diff --git a/aos/network/message_bridge_test.cc b/aos/network/message_bridge_test.cc
index 96003f7..8d52292 100644
--- a/aos/network/message_bridge_test.cc
+++ b/aos/network/message_bridge_test.cc
@@ -7,9 +7,7 @@
 #include "aos/events/pong_generated.h"
 #include "aos/network/message_bridge_client_lib.h"
 #include "aos/network/message_bridge_server_lib.h"
-
-DECLARE_string(override_hostname);
-DECLARE_string(application_name);
+#include "aos/network/team_number.h"
 
 namespace aos {
 namespace message_bridge {