REFACTOR: Replace Ember.controller.inject with import

Puts it more in line with updated ember code

app/assets/javascripts/discourse-loader.js

@@ -7,7 +7,10 @@ var define, requirejs;
     EMBER_MODULES = {
       jquery: { default: $ },
       "@ember/component": { default: Ember.Component },
-      "@ember/controller": { default: Ember.Controller },
+      "@ember/controller": {
+        default: Ember.Controller,
+        inject: Ember.inject.controller
+      },
       "@ember/object": { default: Ember.Object },
       "@ember/routing/route": { default: Ember.Route }
     };