Remove the old root feed files. Bump the db version so rewrite rules can...

Remove the old root feed files. Bump the db version so rewrite rules can regenerate. Don't add these files to old_files to leave them on existing installs. fixes #18384.

git-svn-id: https://core.svn.wordpress.org/trunk@18540 1a063a9b-81f0-0310-95a4-ce76da25c4cd