Use CSS for spacing

Use CSS instead of St.Bin actors for spacing.

https://bugzilla.gnome.org/show_bug.cgi?id=612852

data/theme/gnome-shell.css

@@ -726,6 +726,7 @@ StTooltip {
     border: 0px;
     border-radius: 0px;
     padding: 4px;
+    spacing: 4.5px;
 }
 
 .ws-switcher-active-left {
@@ -744,14 +745,6 @@ StTooltip {
     border-radius: 4px;
 }
 
-.ws-switcher-spacer {
-    width: 0.5px;
-    height: 96px;
-    border: 0px;
-    background: transparent;
-    padding: 4px;
-}
-
 .ws-switcher-box {
     height: 96px;
     border: 2px solid rgba(85,85,85,0.5);

js/ui/workspaceSwitcherPopup.js

@@ -60,11 +60,6 @@ WorkspaceSwitcherPopup.prototype = {
            this._list.add(indicator);
            indicator.set_width(Math.round(indicator.get_height() * this._scaleWidth));
 
-           if (i < global.screen.n_workspaces - 1) {
-               let spacer = new St.Bin({ style_class: 'ws-switcher-spacer' });
-               this._list.add(spacer);
-           }
-
         }
     },