window: Drop some x11-specific apis
The skip-taskbar, skip-pager and urgency hints were only ever implemented for X11, and are not very useful with modern desktops. Relegate the functionality to x11 backend api, and drop the GtkWindow api.
The skip-taskbar, skip-pager and urgency hints were only ever implemented for X11, and are not very useful with modern desktops. Relegate the functionality to x11 backend api, and drop the GtkWindow api.