HPCC-9937 Add ecl-roxie-unused-files --delete option

When delete is specified ("ecl roxie unused-files myroxie --delete")
the unused files found will be deleted from DFS.

Signed-off-by: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>
Merge pull request #6624 from afishbeck/deleteUnusedFiles

HPCC-9937 Add ecl-roxie-unused-files --delete option

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>