I don't know why it is still in there or whether it is a dependency of another xfce4 pkg, you can try removing it from the lists in the pkg-list of the "customize installation" option, but as I said before it has a dependency on webkit2gtk-4.1 which obarun hasn't built, even though the PKGBUILD was provided for it.
Obarun only builds webkit2gtk and it is now a version behind arch, the 4.1 pkg builds easier and faster and satisfies zenity dependency.
zenity itself is a nice pkg that creates gtk windows out of console commands.
When you remove this pkg from the list or force install it without the dependency from console
% sudo pacman -Sdd zenity webkit2gtk-4.1 -r /mnt
then running the installer again completes the installation.
I thought Eric fixed it, obviously he didn't.