Move thickbox styles from wp-admin.css to thickbox.css. Remove old png close icons. Fixes #26178.



git-svn-id: https://develop.svn.wordpress.org/trunk@26395 602fd350-edb4-49c9-b593-d223f7449a82
Remove the new thickbox styles from wp-admin.css. See #26178

git-svn-id: https://develop.svn.wordpress.org/trunk@26396 602fd350-edb4-49c9-b593-d223f7449a82