xmonad: only apply EWMH's logHook extension

- The logHook extension is all that's needed for dunst to display on the
  correct workspace
- Removing the eventHook extension prevents chromium (or any
  application) from abusing _NET_ACTIVE_WINDOW to steal focus

http://xmonad.org/xmonad-docs/xmonad-contrib/XMonad-Hooks-EwmhDesktops.html
xmonad: fix variable shadowing