Avoid including client headers on server builds

src/client/client.h

@@ -36,9 +36,12 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "network/peerhandler.h"
 #include "gameparams.h"
 #include "clientdynamicinfo.h"
-#include <fstream>
 #include "util/numeric.h"
 
+#ifdef SERVER
+#error Do not include in server builds
+#endif
+
 #define CLIENT_CHAT_MESSAGE_LIMIT_PER_10S 10.0f
 
 struct ClientEvent;