I install gnome-shell and Zukitwo-theme. The upper taskbar it is transparent but behind is a bar how can get rid off it. Do I need this bar? See the image!!

you have 2 options.
sudo apt-get remove appmenu-gtk3 appmenu-gtk appmenu-qthave file mangaer handle
desktop if you don't mind not having icons on the desktop.then, log out and login. or hit alt+f2 and enter r to restart the shell.