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

Change-Id: I103575ef6d56a3f50da0c60ca44aacb3f02194e9
diff --git a/aos/network/team_number.cc b/aos/network/team_number.cc
index 8d4e69e..f690943 100644
--- a/aos/network/team_number.cc
+++ b/aos/network/team_number.cc
@@ -5,11 +5,11 @@
 #include <unistd.h>
 #include <stdlib.h>
 
-#include "glog/logging.h"
-
 #include "aos/util/string_to_num.h"
 
-DECLARE_string(override_hostname);
+DEFINE_string(override_hostname, "",
+    "If set, this forces the hostname of this node to be the provided "
+    "hostname.");
 
 namespace aos {
 namespace network {