HPCC-11324 - Allow DFS to delete external file via logical ref.

Permit a couple of couple of places to delete external files

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #5786 from jakesmith/hpcc-11324

HPCC-11324 - Allow DFS to delete external file via logical ref.

Reviewed-By: Gavin Halliday <gavin.halliday@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>