PG: always clear_primary_state when leaving Primary

Otherwise, entries from the log collection process might leak into the next
epoch, where we might end up choosing a different authoritative log.  In this
case, it resulted in us not rolling back to log entries on one of the replicas
prior to trying to recover from an affected object due to the peer_missing not
being cleared.

Fixes: #10059
Backport: giant, firefly, dumpling
Signed-off-by: Samuel Just <sjust@redhat.com>