Remove media browser from Rich Text

[balsama]

While super cool, embedding media in a rich text area discourages structured content best practices. It also makes it difficult (impossible?) to get the resource in a single request via the API since Drupal doesn't treat the referenced media item isn't a true relationship. A consumer would need to make several round trip requests to get a media item embedded in a rich text area.

We should encourage users of Headless to structure their data with media references and remove support for directly embedding media in rich text areas.