Twenty Fourteen: remove unused class name, props obenland. See #25946.

git-svn-id: https://develop.svn.wordpress.org/trunk@26151 602fd350-edb4-49c9-b593-d223f7449a82
Twenty Fourteen: simplify and prefix post thumbnail sizes, props obenland. See #25946.

git-svn-id: https://develop.svn.wordpress.org/trunk@26152 602fd350-edb4-49c9-b593-d223f7449a82