DEV: glimmerify discourse-root (#17390)

As a result discourse-root will be tag-less

app/assets/javascripts/discourse/app/components/discourse-root.js

@@ -1,11 +1,3 @@
-import Component from "@ember/component";
+import GlimmerComponent from "discourse/components/glimmer";
 
-let componentArgs = { tagName: "div" };
+export default class DiscourseRoot extends GlimmerComponent {}
-
-// TODO: Once we've moved to Ember CLI completely we can remove this block
-// eslint-disable-next-line no-undef
-if (!Ember.FEATURES.EMBER_GLIMMER_SET_COMPONENT_TEMPLATE) {
-  componentArgs = { tagName: "" };
-}
-
-export default Component.extend(componentArgs);