Put back "max-width: 100%" for all <select> in the admin. Doesn't seem to work...

Put back "max-width: 100%" for all <select> in the admin. Doesn't seem to work for IE7 but doesn't seem to break anything either. Props Master Jake, fixes #19613

git-svn-id: https://core.svn.wordpress.org/trunk@20626 1a063a9b-81f0-0310-95a4-ce76da25c4cd