Partially back out changeset 5273, ticket 5181

[rubys]

2.4-bleeding has been deployed on wordpress.com which exposes a problem with the patch associated with ​ticket 5181. This ticket partially backs that change out until a proper fix can be made.

The root issue is that the app support and the rest of wp produce feeds differently, and in the process interpret the database differently. The app support will put HTML in $post->post_content, but the rest of wordpress assumes that the post_content contains text which, after passed through various filters, produces html. This is a subtle difference which doesn't show up immediately, but the simple presence of blank lines will cause the two to produce noticeably different results.

For app to function properly, there needs to be a way to "unfilter" (x)html, i.e., a way to reverse engineer what text would produce the equivalent of a given (x)html result after filtering. But to that proper fix will take time, so meanwhile the 2.3 functionality should be restored

[ryan]

(In [6315]) Back out some changes from #5181. Props rubys. fixes #5307