Revert "JounralingObjectStore: journal->committed_thru after replay"

committed_thru can race with the sync thread.

This reverts commit d8d27f13e11dcaefd3aa1c049b97c980283da575.
Reviewed-by: Greg Farnum <greg@inktank.com>
Merge branch 'next'
Merge git://github.com/ceph/ceph