DEV: Pass post instead of transformedPost to post-bottom-ad (#199)

Changes in 0948d6b caused the post-bottom-ad component to start receiving the widget-ised 'transformedPost' instead of the original `post` model. In most cases this difference didn't matter, but it did cause noticable issues with `@model.category` and `@model.topic`.

This commit also deletes the unused `post-bottom/discourse-adplugin.hbs` connector. In the past, the adplugin itself was defining the post-bottom outlet. But now, we use RenderGlimmer to load the `post-bottom-ad` directly.

assets/javascripts/discourse/initializers/initialize-ad-plugin.js

@@ -14,7 +14,7 @@ export default {
 
     withPluginApi("0.1", (api) => {
       api.decorateWidget("post:after", (helper) => {
-        return helper.attach("after-post-ad", helper.attrs);
+        return helper.attach("after-post-ad", helper.widget.model);
       });
     });