Update to use the loglist v3 schema everywhere

[aarongable]

The loglist3 package appears complete and is in use in a few places
throughout the repository. However, most of the repo still relies on the
loglist2 package. Although Chrome is still publishing log lists in both
formats, it seems appropriate to update the preponderance of usage to
the new schema.

This also adds a v3-formatted testdata file, with the same contents as
the corresponding v2 file. (This file will need to be updated when the
//ctpolicy/chromepolicy.go logic is updated, as it does not contain enough
different operator groups to truly exercise the new Chrome policy, but
that is an issue for #906).

Checklist

• I have updated the CHANGELOG.
  • It doesn't seem to be necessary for a change this internal?
• I have updated documentation accordingly.

[pav-kv]

/gcbrun

[roger2hk]

/gcbrun

[roger2hk]

Thank you very much for the PR. LGTM with some minor comments.

[roger2hk]

/gcbrun