mpris: Hide unused elements to leave more space for the title

The Message class this is derived from unconditionally adds a close
button with 0 opacity that only gets shown on hover for messages that
can actually be closed. The MPRIS MediaMessage however can never be
closed and having a close button can cause the title to be cut short
unexpectedly.

Similarly the secondary text which other notifications use to display
the notification time is always left empty here as well.

https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/3664

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1632>

js/ui/mpris.js

@@ -28,6 +28,10 @@ class MediaMessage extends MessageList.Message {
         this._icon = new St.Icon({ style_class: 'media-message-cover-icon' });
         this.setIcon(this._icon);
 
+        // reclaim space used by unused elements
+        this._secondaryBin.hide();
+        this._closeButton.hide();
+
         this._prevButton = this.addMediaControl('media-skip-backward-symbolic',
             () => {
                 this._player.previous();