Allow Jetpack CDN to Service Images

[efuller]

Description

Currently, if a site is using Jetpack boost to serve up images, when a cover image is set to be used, the image is served from the origin, not the Jetpack boost CDN.

There is code in place that strips out the Jetpack CDN URL. This code should be removed and we should use what WordPress gives us natively.

Use Case

When a user sets an Apple News cover image it is served with the correct URL. If Jetpack Boost is being used, it should serve the image from the CDN

[efuller]

A working branch has been created - https://github.com/alleyinteractive/apple-news/tree/feature/allow-jetpack-cdn-serve-images - which includes a fix. If I recall, there will need to be a bit more work done in order for unit tests to pass.

I would also recommend a round of manual testing as well.