livesys-main: Don't create liveuser on GNOME
    
    GNOME is going to be creating the liveuser from gnome
    initial setup from now on and also handling starting the
    installer from there as well.
    
    This commit changes the livesys scripts to not create the liveuser
    account or try to use the liveuser home directory.
    
    It also turns off fedora-welcome and turns back on gnome-tour.