Revert "Work around FeedPress's default XSL"

This reverts commit cc87791524aedd593cff5a74532befe7ab69ce9d.

Although the CloudFlare page rule did produce a 302 as expected for
/~files/atom.xsl, redirecting the user here to /files/atom.xsl, Chrome
seemed to fail in actually respecting the redirect. Possibly a bug in
the way that `<?xml-stylesheet ... ?>` directives are handled.