Feature: make "join game" button join the game, instead of first showing a lobby window (#9467)

Nobody really paid attention to the lobby window, and it completely
missed its purpose. Most people don't even wait for companies to
show up, but just hit "New Company".
This in turn means people create a lot of unneeded companies, while
they "just want to watch the game" or join another company.

Instead, "Join Game" now just joins the game as spectators.

src/network/network_internal.h

@@ -94,7 +94,6 @@ extern uint8 _network_reconnect;
 extern CompanyMask _network_company_passworded;
 
 void NetworkQueryServer(const std::string &connection_string);
-void NetworkQueryLobbyServer(const std::string &connection_string);
 
 void GetBindAddresses(NetworkAddressList *addresses, uint16 port);
 struct NetworkGameList *NetworkAddServer(const std::string &connection_string, bool manually = true, bool never_expire = false);