notifications: Never use source icon for notifications

With the new design we will show the source icon in the header of a
notification.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3103>

data/theme/gnome-shell-sass/widgets/_message-list.scss

@@ -77,12 +77,6 @@
       icon-size: $large_icon_size;
       -st-icon-style: symbolic;
     }
-
-    // fallback
-    > .fallback-app-icon {
-      width: $base_icon_size;
-      height: $base_icon_size;
-    }
   }
 
   // content

js/ui/calendar.js

@@ -798,7 +798,7 @@ class NotificationMessage extends MessageList.Message {
                 icon_size: MESSAGE_ICON_SIZE,
             });
         } else {
-            return this.notification.source.createIcon(MESSAGE_ICON_SIZE);
+            return null;
         }
     }
 

js/ui/mpris.js

@@ -72,9 +72,6 @@ class MediaMessage extends MessageList.Message {
             let file = Gio.File.new_for_uri(this._player.trackCoverUrl);
             this._icon.gicon = new Gio.FileIcon({file});
             this._icon.remove_style_class_name('fallback');
-        } else if (this._player.app) {
-            this._icon.gicon = this._player.app.icon;
-            this._icon.add_style_class_name('fallback');
         } else {
             this._icon.icon_name = 'audio-x-generic-symbolic';
             this._icon.add_style_class_name('fallback');

js/ui/notificationDaemon.js

@@ -212,12 +212,8 @@ class FdoNotificationDaemon {
             });
         }
 
-        // 'image-data' (or 'image-path') takes precedence over 'app-icon'.
         let gicon = this._imageForNotificationData(hints);
 
-        if (!gicon)
-            gicon = this._iconForNotificationData(appIcon);
-
         if (!gicon)
             gicon = this._fallbackIconForNotificationData(hints);
 
@@ -278,7 +274,8 @@ class FdoNotificationDaemon {
             ? MessageTray.PrivacyScope.SYSTEM
             : MessageTray.PrivacyScope.USER);
 
-        let sourceGIcon = source.useNotificationIcon ? gicon : null;
+        // Only fallback to 'app-icon' when the source doesn't have a valid app
+        const sourceGIcon = source.app ? null : this._iconForNotificationData(appIcon);
         source.processNotification(notification, sourceGIcon);
     }
 
@@ -337,8 +334,6 @@ class FdoNotificationDaemonSource extends MessageTray.Source {
 
         if (this.app)
             this.title = this.app.get_name();
-        else
-            this.useNotificationIcon = true;
 
         if (sender) {
             this._nameWatcherId = Gio.DBus.session.watch_name(sender,