HPCC-11195 Suppress creation of unread spill files in Roxie

Code generator should not be creating them, but this should render them
harmless if it does.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #5723 from richardkchapman/roxie-spill-hack

HPCC-11195 Suppress creation of unread spill files in Roxie

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>