10f7344336
Since commit a4660293748, the activities button uses the standard `:checked` pseudo class in the overview instead of the custom `:overview`. As a side effect, the generic handling of the `CHECKED` Atk state in StWidget now covers the case, and we no longer need to manage the state explicitly. Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3126>