Remove duplicate of the 'oembed_providers' filter accidentally introduced in [28949].

Move annoted table of oEmbed providers into the existing filter docs.

See #28507.
Fixes #28372. 

Built from https://develop.svn.wordpress.org/trunk@28950


git-svn-id: http://core.svn.wordpress.org/trunk@28747 1a063a9b-81f0-0310-95a4-ce76da25c4cd