config: remove redundant notification-icon-size option

src/configModel/configModel.vala

@@ -659,13 +659,6 @@ namespace XimperShellNotificationCenter {
             get; set; default = "single";
         }
 
-        /**
-         * Notification icon size, in pixels.
-         */
-        [Version (deprecated = true, replacement = "CSS root variable")]
-        public int notification_icon_size {
-            get; set; default = -1;
-        }
 
         /**
          * Notification body image height, in pixels.

src/notification/notification.vala

@@ -693,19 +693,6 @@ namespace XimperShellNotificationCenter {
             }
 
 
-            int notification_icon_size =
-                ConfigModel.instance.notification_icon_size.clamp (-1, int.MAX);
-            if (notification_icon_size < 1) {
-                notification_icon_size = -1;
-            }
-            img.set_pixel_size (notification_icon_size);
-            img.height_request = notification_icon_size;
-            img.width_request = notification_icon_size;
-            int app_icon_size = (notification_icon_size / 3).clamp (-1, int.MAX);
-            if (app_icon_size < 1) {
-                app_icon_size = -1;
-            }
-            img_app_icon.set_pixel_size (app_icon_size);
 
             bool img_path_is_theme_icon = false;
             bool img_path_exists = File.new_for_uri (param.image_path ?? "").query_exists ();