From ceph mimic (13.x) onwards, `mds deactivate` command is
deprecated. To scale down the number of active MDSes of a filesystem,
it's sufficient to set the desired number of active MDSes using
'max_mds' setting, and is no longer required to individually
deactivate the unwanted MDSes.
Resolves: #2725
Signed-off-by: Ramana Raja <rraja@redhat.com>