Revert "FIX: body class from category not loadeing on topics on first load"

This reverts commit d15b698ac9.

app/assets/javascripts/discourse/views/navigation-category.js.es6

@@ -0,0 +1,5 @@
+import AddCategoryClass from 'discourse/mixins/add-category-class';
+
+export default Em.View.extend(AddCategoryClass, {
+  categoryFullSlug: Em.computed.alias('controller.category.fullSlug')
+});