Remove: old server listing via Master Server

This removes all UDP from the game except for a local broadcast
to find LAN games.

So long Master Server, and tnx for all the fish!

src/network/network_udp.h

@@ -14,8 +14,6 @@
 
 void NetworkUDPInitialize();
 void NetworkUDPSearchGame();
-void NetworkUDPQueryMasterServer();
-void NetworkUDPQueryServer(const std::string &connection_string, bool manually = false);
 void NetworkUDPClose();
 void NetworkUDPServerListen();
 void NetworkBackgroundUDPLoop();