notmuch-report.json: Remove oci::motion from accepted/rejected

notmuch-report.json: Remove oci::motion from accepted/rejected

This will show one or two entries per accepted/rejected motion thread:

1. The initial proposal will always be shown.
2. If there was a "this proposal was accepted/rejected" post, that is
   shown too.

If folks follow my suggested:

  [{project} {status}]: {motion description} (+{LGTMs} -{REJECTs} #{ABSTAINs})

subject template, you won't even have to visit the message to see the
vote breakdown.