Access class directly instead of using `this` in the `shortcodeAttrs` method of any factory-generated `wp.media.collection`.

Fixes #27183.


Built from https://develop.svn.wordpress.org/trunk@27238


git-svn-id: http://core.svn.wordpress.org/trunk@27095 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/js/media-editor.js

@@ -406,7 +406,7 @@
 			}
 
  			// Remove default attributes from the shortcode.
- 			_.each( this.defaults, function( value, key ) {
+ 			_.each( wp.media[prop].defaults, function( value, key ) {
  				if ( value === attrs[ key ] ) {
  					delete attrs[ key ];
 				}