removed xinerama-enabled dmenu action

I don't think we're going to see any Xinerama support upstream, at least not
anytime soon. It doesn't make sense to ship something with xmonad that isn't
going to work out of the box. So for now Xinerama users should just use this
patch: http://www.jcreigh.com/xmonad/xinerama-dmenu.html

Operations.hs

@@ -253,13 +253,3 @@ restart = do
     prog <- getProgName
     args <- getArgs
     executeFile prog True args Nothing
-
--- | Starts dmenu on the current screen. (Requires patches to dmenu for the -x
--- and -w options.)
-dmenu :: X ()
-dmenu = do
-    XState { xineScreens = xinesc, workspace = ws } <- get
-    let curscreen = fromMaybe 0 (M.lookup (W.current ws) (W.ws2screen ws))
-        sc = xinesc !! curscreen
-    spawn $ concat [ "exe=`dmenu_path | dmenu -x ", show (rect_x sc)
-                   , " -w " , show (rect_width sc) , "` && exec $exe" ]