Cleanup after [29179]:

* Remove `wp.media.mixin.pauseAllPlayers()` - was only ever intended to be used in MCE views, reaches too far into global scope. Rendered irrelevant since [28364].
* Remove `wp.media.mixin.pausePlayers()` - added in [28364]. MCE views no longer keep track of player instances and call mixin methods, they refer to their child iframes and call MEjs methods on the iframe's `window.mejs.players`. 

See #28905.

Built from https://develop.svn.wordpress.org/trunk@29194


git-svn-id: http://core.svn.wordpress.org/trunk@28978 1a063a9b-81f0-0310-95a4-ce76da25c4cd