userMenu: belatedly rename CSS to match the new filename

https://bugzilla.gnome.org/show_bug.cgi?id=651299

data/theme/gnome-shell.css

@@ -371,7 +371,7 @@ StTooltip StLabel {
     -boxpointer-gap: 4px
 }
 
-#panelStatusMenu {
+#panelUserMenu {
     spacing: 4px;
 }
 

js/ui/userMenu.js

@@ -368,7 +368,7 @@ UserMenuButton.prototype = {
 
     _init: function() {
         PanelMenu.Button.prototype._init.call(this, 0.0);
-        let box = new St.BoxLayout({ name: 'panelStatusMenu' });
+        let box = new St.BoxLayout({ name: 'panelUserMenu' });
         this.actor.set_child(box);
 
         this._lockdownSettings = new Gio.Settings({ schema: LOCKDOWN_SCHEMA });