user groups: Send only updated attribute for user group updates.

Earlier PATCH user_groups/<int:user_group_id> required
both name and description parameters. So we had to send
them in patch requests even if just one of the attribute
was updated.

As the endpoint is now updated we send only those parameters
that are changed.

web/src/user_group_edit.js

@@ -274,13 +274,9 @@ export function initialize() {
         }
         if (new_name !== group.name) {
             data.name = new_name;
-        } else {
-            data.name = group.name;
         }
         if (new_description !== group.description) {
             data.description = new_description;
-        } else {
-            data.description = group.description;
         }
 
         const $status_element = $(".group_change_property_info");