Glade misleads us into thinking we need these, but the
property is somewhat confusing in GTK3. In general we don't
want `can-focus` to be true for containers, as that will
break keynav for the children. For non-containers, the
defaults are appropriate.
Instead of manually setting `can-focus`, we should just
use the default values. GTK has sane defaults.
Fixes https://gitlab.gnome.org/GNOME/calls/-/issues/366
