[27640] supported a caption for audio and video shortcodes as part of a UX iteration for the related MCE views. These captions have since be excluded, so the extra code should be removed (it was there for this sole reason).

See #27320.



git-svn-id: https://develop.svn.wordpress.org/trunk@27979 602fd350-edb4-49c9-b593-d223f7449a82
Only set the `poster` attribute automatically for videos when the image does not match the default mime-type icon. `wp_prepare_attachment_for_js()` is used in multiple contexts. This context requires disambiguation.

See [27659].



git-svn-id: https://develop.svn.wordpress.org/trunk@27980 602fd350-edb4-49c9-b593-d223f7449a82