Revert attachment.url back to props.url. Fixes error that prevents inserting media into the editor.

see #24046


git-svn-id: http://core.svn.wordpress.org/trunk@24009 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Compress scripts/styles: 3.6-beta1-24010.

git-svn-id: http://core.svn.wordpress.org/trunk@24010 1a063a9b-81f0-0310-95a4-ce76da25c4cd