remove old versions

git-svn-id: https://plugins.svn.wordpress.org/jetpack-markdown/trunk@896194 b8457f37-d9ea-0310-8a92-e5e31aec5664
tested on 3.9

git-svn-id: https://plugins.svn.wordpress.org/jetpack-markdown/trunk@896196 b8457f37-d9ea-0310-8a92-e5e31aec5664