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>
Merge pull request #2843 from dachary/wip-9752-past-intervals

osd: past_interval display bug on acting

Reviewed-by: Greg Farnum <greg@inktank.com>