Change 'Width' to 'Layout' to match the hard-coded list of translatable theme...

Change 'Width' to 'Layout' to match the hard-coded list of translatable theme features in get_theme_feature_list().

props janrenn.
fixes #26777 for trunk.
Built from https://develop.svn.wordpress.org/trunk@26905


git-svn-id: https://core.svn.wordpress.org/trunk@26788 1a063a9b-81f0-0310-95a4-ce76da25c4cd