Monitor: don't set arrays dirty after transition to read-only

Monitor: don't set arrays dirty after transition to read-only

This patch reverts commit 4867e068. Setting arrays dirty after
transition from inactive to anything else causes unnecessary
meta data writes and may wreak trouble unnecessarily when
a disk was missing during assembly but the array was never
written to.

The reason for 4867e068 was a special situation during reshape
from RAID0 to RAID4. I ran all IMSM test cases with it reverted
and found no regressions, so I believe the reshape logic for
IMSM works fine in mdadm 3.3 also without this.

Signed-off-by: Martin Wilck <mwilck@arcor.de>
Signed-off-by: NeilBrown <neilb@suse.de>