Fix catalog zone reconfiguration crash

Fix catalog zone reconfiguration crash

The following scenario triggers a "named" crash:

1. Configure a catalog zone.
2. Start "named".
3. Comment out the "catalog-zone" clause.
4. Run `rndc reconfig`.
5. Uncomment the "catalog-zone" clause.
6. Run `rndc reconfig` again.

Implement the required cleanup of the in-memory catalog zone during
the first `rndc reconfig`, so that the second `rndc reconfig` could
find it in an expected state.

(cherry picked from commit 43ac2cd229813c04438e027c42c0b93b9661adda)