workspaceSwitcherPopup: Drop direction parameter

The original popup included arrows that indicated the direction of
the switch. We stopped doing that a long time ago, and ever since
the popup has only indicated active vs. non-active workspaces.

Simplify both the API and style to reflect that.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2127>

js/ui/windowManager.js

@@ -1820,7 +1820,7 @@ var WindowManager = class {
                     this._isWorkspacePrepended = false;
                 });
             }
-            this._workspaceSwitcherPopup.display(direction, newWs.index());
+            this._workspaceSwitcherPopup.display(newWs.index());
         }
     }