HPCC-11786 Roxie cored when processing a file notification

When a CResolvedFile was released (because no query uses it any
more), the subscription to dali for the superfile remained active.
This would result in a core if the superfile was subsequently updated

Also added the ability to disable the superfile subscription system.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #6139 from richardkchapman/roxie-superfile-unsubscribe

HPCC-11786 Roxie cored when processing a file notification

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>