HPCC-10742 - Ensure in-progress partial output is removed

If a write output is aborted, the partial file was not being
deleted.
NB: If the process died on the other hand, the CFIPScope did
ensure the partial file was deleted.

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #5357 from jakesmith/hpcc-10742

HPCC-10742 - Ensure in-progress partial output is removed

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>