Revert "window-list: Only initialize preview visibility on map"

It is not possible to unmap an actor from within the map vfunc,
so the fix broke the initial visibility again.

This reverts commit 8b7cfff558.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell-extensions/-/merge_requests/292>

extensions/window-list/workspaceIndicator.js

@@ -43,6 +43,7 @@ class WindowPreview extends St.Button {
             },
             'notify::minimized', this._updateVisible.bind(this),
             this);
+        this._updateVisible();
 
         global.display.connectObject('notify::focus-window',
             this._onFocusChanged.bind(this), this);
@@ -54,12 +55,6 @@ class WindowPreview extends St.Button {
         return this._window;
     }
 
-    vfunc_map() {
-        super.vfunc_map();
-        // initialize visibility after being added to the stage
-        this._updateVisible();
-    }
-
     _onFocusChanged() {
         if (global.display.focus_window === this._window)
             this.add_style_class_name('active');