I'm wondering where I can re-set this function (zoom out and show all workspaces) in elementary OS?
You can change the key
gsettings in a terminal window. It defaults to
['<Super>Down', '<Super>s'] so if you only want to disable Super+s you can set it to
[<Super>Down] for instance.
$ gsettings set org.gnome.desktop.wm.keybindings show-desktop "['<Super>down']"