You can right-click the Deja Vu icon inside System Preferences and choose "Remove "Deja Vu" Preference Pane"
It also resides inside '/Library/Contextual Menu Plugins' - I think. I can't remember. Maybe it hides inside your 'Home folder/Library/Contextual Menu Plugins'
You have to relaunch Finder by either logging out and back in or by holding down Option and right clicking the Finder icon in the Dock.