Themes: Remove some unused CSS (we have neither a .theme-categories or .theme-linear-grid). See #25948


git-svn-id: https://develop.svn.wordpress.org/trunk@26463 602fd350-edb4-49c9-b593-d223f7449a82
Themes: Update the responsive layouts for the Search box after r26461. See #26305


git-svn-id: https://develop.svn.wordpress.org/trunk@26464 602fd350-edb4-49c9-b593-d223f7449a82