prevent theme to apply `border-radius` to admin-bar search field; removed `border-radius` from `#wpadminbar .screen-reader-shortcut`; added rtl styles for new admin-bar searchh icon; removed unnecessary admin-bar rtl styles

git-svn-id: https://plugins.svn.wordpress.org/mp6/trunk@747093 b8457f37-d9ea-0310-8a92-e5e31aec5664