osd: past_interval display bug on acting

The acting array was incorrectly including the primary and up_primary.

http://tracker.ceph.com/issues/9752 Fixes: #9752

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
(cherry picked from commit c5f8d6eded52da451fdd1d807bd4700221e4c41c)
Merge pull request #2846 from dachary/wip-9752-past-intervals-giant

osd: past_interval display bug on acting