Cleans the MOB files when they're expired and their min versions are 0.
If the latest timestamp of Cells in a MOB file is older than the TTL in the column family,
it's regarded as expired. This cleaner deletes them.
At a time T0, the cells in a mob file M0 are expired. If a user starts a scan before T0, those
mob cells are visible, this scan still runs after T0. At that time T1, this mob file M0
is expired, meanwhile a cleaner starts, the M0 is archived and can be read in the archive