zdb: don't print log spacemap stats in pools without the feature

Creating a pool with not features enabled and running
`zdb -mmmmmm on` it before the patch:

```
Log Space Maps in Pool:

Log Space Map Obsolete Entry Statistics:
0        valid entries out of 0        - txg 0
0        valid entries out of 0        - total
```

After this patch the above output goes away.

Reviewed by: Matt Ahrens <[email protected]>
Reviewed by: Sara Hartse <[email protected]>
Reviewed by: Brian Behlendorf <[email protected]>
Signed-off-by: Serapheim Dimitropoulos <[email protected]>
Closes #9048 

0 files changed, 0 insertions, 0 deletions