PlayerSAO saving fix (#4734)

PlayerSAO::disconnected() function was historical and remove the link between SAO and RemotePlayer session. With previous attributes linked to RemotePlayer saving was working. But now attributes are read from SAO not RemotePlayer and the current serialize function verify SAO exists to save the player attributes.

Because PlayerSAO::disconnected marks playersao for removal, only mark playerSAO for removal and let PlayerSAO::removingFromEnvironment do the correct saving behaviour and all the disconnection process instead of doing a partial removal and let the server loop doing the RemotePlayer cleanup and remove some saved attributes...