core/testdata: Replace feeds.xml with Goliath-generated export OPML.
core/testdata: Replace feeds.xml with Goliath-generated export OPML.

The minor differences are:
  - OPML export is correctly marked as conforming to OPML 2.0 standard.
  - Feeds tags are not self-closing. Both ways are legal in XML but the
    latter is not supported in the Go XML marshaller yet.
  - In one feed, the apostrophe character was previously not XML-encoded
    and now is. Upon import, this data is transformed to UTF-8, so the
    database layer still correctly stores an actual apostrophe
    character.

jrupac/goliath,jrupac/goliath,jrupac/goliath,jrupac/goliath,jrupac/goliath