This vfunc override has been introduced to ensure app icons are always
squared, but since the container of the AppIcon gets a square allocation
anyway if the 'square' property of the SwitcherButton is set, there's
no need to return a special width here.
Without the override we can also stop setting the size of the iconBin
manually. And since shell_app_create_icon_texture() uses logical pixels
but clutter_actor_set_size() uses screen pixels, that means we now no
longer set the size of the icon back to the unscaled value after it was
already correct.
Fixes https://gitlab.gnome.org/GNOME/gnome-shell/issues/1325
(cherry picked from commit 074129682bc134f4ca0005a8d9edef210e30da69)
ae05679498