osd: Remove unused checkpoint code

Signed-off-by: David Zafman <david.zafman@inktank.com>
osd: hit_set_persist(): Verify all objects aren't degraded

Fixes: #7592

Signed-off-by: David Zafman <david.zafman@inktank.com>
Merge pull request #1429 from ceph/wip-7592-final

Wip 7592 final

Reviewed-by: Sage Weil <sage@inktank.com>