reflect recent changes in the pg deletion logic

No need to wait on DeletingStateRef for flush https://github.com/ceph/ceph/commit/d3dd99b725afaa026fe6f700ddc14a7f657f2170
Fix typos

http://tracker.ceph.com/issues/5058 refs #5058

Signed-off-by: Loic Dachary <loic@dachary.org>