Twenty Fifteen: make font-size/line-height in editor-style.css the same as in style.css. Remove margins from the editor body, interferes with autoresize in some browsers and is overriden in the default styles. See #29799

git-svn-id: https://develop.svn.wordpress.org/trunk@29909 602fd350-edb4-49c9-b593-d223f7449a82