Revert "Revert "DEV: Remove Discourse.Route""

This reverts commit b4d27d3.

Plugins have been updated to not use this anymore.

app/assets/javascripts/discourse/app/routes/discourse.js

@@ -2,7 +2,6 @@ import { once } from "@ember/runloop";
 import Composer from "discourse/models/composer";
 import { getOwner } from "discourse-common/lib/get-owner";
 import Route from "@ember/routing/route";
-import deprecated from "discourse-common/lib/deprecated";
 import { seenUser } from "discourse/lib/user-presence";
 
 const DiscourseRoute = Route.extend({
@@ -113,14 +112,4 @@ const DiscourseRoute = Route.extend({
   }
 });
 
-Object.defineProperty(Discourse, "Route", {
-  get() {
-    deprecated("Import the Route class instead of using Discourse.Route", {
-      since: "2.4.0",
-      dropFrom: "2.5.0"
-    });
-    return Route;
-  }
-});
-
 export default DiscourseRoute;