ui: Remove explicit can-focus

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

src/ui/in-app-notification.ui

@@ -9,17 +9,14 @@
     <child>
       <object class="GtkBox">
         <property name="visible">True</property>
-        <property name="can_focus">False</property>
         <child>
           <object class="GtkButton">
             <property name="visible">True</property>
-            <property name="can_focus">True</property>
             <property name="receives_default">True</property>
             <signal name="clicked" handler="calls_in_app_notification_hide" swapped="yes"/>
             <child>
               <object class="GtkImage">
                 <property name="visible">True</property>
-                <property name="can_focus">False</property>
                 <property name="icon_name">window-close-symbolic</property>
               </object>
             </child>
@@ -34,7 +31,6 @@
         <child>
           <object class="GtkLabel" id="label">
             <property name="visible">True</property>
-            <property name="can_focus">False</property>
             <property name="wrap">True</property>
             <property name="margin-left">24</property>
             <property name="margin-right">24</property>