Plugin install: Remove columns and screen options.

fixes #28803.
Built from https://develop.svn.wordpress.org/trunk@29498


git-svn-id: http://core.svn.wordpress.org/trunk@29276 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Autoprefixer for [29496].

see #28844.
Built from https://develop.svn.wordpress.org/trunk@29499


git-svn-id: http://core.svn.wordpress.org/trunk@29277 1a063a9b-81f0-0310-95a4-ce76da25c4cd