dm persistent data: remove debug space map checker

dm persistent data: remove debug space map checker

Remove debug space map checker from dm persistent data.

The space map checker is a wrapper for other space maps that double
checks the reference counts are correct.  It holds all these reference
counts in memory rather than on disk, so uses a lot of memory and is
thus restricted to small pools.

As yet, this checker hasn't found any issues, but has caused a few of
its own due to people turning it on by default with larger pools.

Removing.

Signed-off-by: Joe Thornber <[email protected]>
Signed-off-by: Mike Snitzer <[email protected]>
Signed-off-by: Alasdair G Kergon <[email protected]>