UICommon/NetPlayIndex: Allow move semantics in SetGame()

If the parameter is const, then a move won't actually be able to occur,
making the std::move non-functional. We can remove the const qualifier
to remedy this.

Source/Core/UICommon/NetPlayIndex.cpp

@@ -221,7 +221,7 @@ void NetPlayIndex::SetPlayerCount(int player_count)
   m_player_count = player_count;
 }
 
-void NetPlayIndex::SetGame(const std::string game)
+void NetPlayIndex::SetGame(std::string game)
 {
   m_game = std::move(game);
 }